Geez Pat, I hardly know where to start.  

One thing I can virtually guarantee will be hands-free auto-hover, giving
it a substantial leg up on the more manual competition.  

Assuming it's hydrogen powered, it might have that exciting new feature
where trace amounts of this fuel are extracted from the atmosphere as you
fly along. What could be more satisfying than a free fill-up?

Somewhat less efficient process should you choose to drive. Of course
driving entails other challenges as you might expect being on the ground
among the land-bound riff raff, and that's only if you've been trained in
that arcane practice.

Full environmental controls which sense minute changes in skin temperature
and respiratory rate of each occupant directing the perfect conditioned
and oxygen enriched air flow right where it's needed.

Not new, but still of great value is the full suite of accident avoidance
sensors and devices.  Between the direct link to the GPS system and the
LASER scanning and ranging monitors tied right into the propulsion and
guidance sub-systems making it actually impossible to collide or crash,
even if you try!

Something else that's been out for quite a while, but only on the better
engineered vehicles is nearly organic homeostasis and self-repair.  A
matrix of sensors and active probes feeding into the on-board quantum
computer detects the smallest degradation and risk of failure, invoking
either a corrective nano-bot to restore equilibrium, or to effect repair.

One interesting twist on the above is rumored to be introduced on the 2071
models - perpetual updating.  Sure these vehicles will cost substantially
more, should they actually reach market, but it's a one-time purchase.
The absolutely cutting-edge nanotechnology will be capable of implementing
not only adjustments that would otherwise have required a recall, but will
actually be able to "re-manufacture" the car on the fly to continuously
provide all current features.

For the first time you'll be able to pass your Miata along to offspring or
purchasers with their confidence that what they are receiving will be
identical to what's in the showroom at the very moment.

All the expected entertainment and creature-comfort features that are
options on lesser vehicles are standard on this Mazda, the pride of China:

    Interfacing with the Global Entertainment Enterprise - World Integrative
    Zone, also known as, that's right,  GEE-WIZ.  All the music and holorama
    spectacles you could hope to find, including the collaborative and
    interactive world-wide-jam network.  Beauty here is you could be flying
    along (another reason to not bother with driving) and plug your interface
    controller into the collaboration console and suddenly find yourself
    engaged in microtonal explorations with a stranger in the Chinese
    Hemisphere. How cool is that?

    Full food synthesis capability, but not just those lifeless supplement
    cubes, but actual organic meals including synfruit, synveggies, synmeats,
    and a rich choice of beverages including the most popular psychotropic
    and stimulicious proto-fluids to replenish while they refresh, thank
    PepsiSan.

    Even though the worst of the terrorism that plagued the last seven
    decades has finally been brought under control through the repentant
    George WHW Bush, president of the Non-Chinese Hemisphere and his War on
    the War on Terror along with the aggressive genetic re-engineering and
    extensive lacing of the food and water supply with all manner of
    controlling and reformative medicaments, this new beauty is fully
    equipped with the latest in defensive and offensive weaponry.  Should
    something even as crude as a missile be fired in your direction, it would
    be detected virtually at launch and immediately destroyed by a
    high-energy particle beam, followed by a close-radius painting of the
    launch area with energetic neutrons and helium nuclei - no threat from
    that area again.

    Finally, and this rumor is truly treading the edge of fantasy and folly,
    some believe Mazda has finally perfected the Flux Capacitor after
    digitally enhancing the entire series of Back To The Future, cloning
    Michael J. Fox and Christopher Lloyd, and pouring billions of credits
    into the two MIT research centers - Midway Institute of Technology and
    Manila Institute of Technology.  Thankfully, the Mr. Fusion power supply
    wasn't needed due to the impressive advances in hydrogen and enhanced
    hydrogen technology.  

    I mean, how would you like to beam into your beloved Mazda Miata MX-5243,
    strap on the brain-wave interface headband, think her into a lazy banked
    turn at 50,000 feet, kick in the Flux Capacitor and find yourself in the
    year 2007?  Imagine, the streets are maintained, many folks - rich and
    poor alike are still living on the ground, Miatas of that time running on
    gasoline I believe they called it, before the earth's petroleum reserves
    were depleted, had to be driven as they so quaintly characterized it, had
    a TOP speed of 130 miles per hour, or roughly the stall velocity of your
    MX-5243, those awful collisions and crashes, oh the humanity!.  But just
    picture the look on the faces of these primitives as they caught sight of
    your mind-boggling mechanical perfection.  A caution however, they were
    quite savage in those days, led by and under the influence of power
    hungry and ignorant leadership.  Should they get their greasy hands on
    you, even for a moment, you might never get back to the future...

Frank

It will run on frijoleum, currently the most powerful fuel known to
man.  There will be a passage built into the seat that will direct the
gas directly to the intake, raising the 1.6 to around 3,500 hp @
2,500rpm.  The range of the vehicle will depend entirely on the
quantity of refried beans (frijoles) eaten before the trip....

Next question?

Taking specifically from Douglas Adams, we know it will be:

a) Extremely improbable, and

b) black. :)

miker

It will fly and fold up into an attache case meaning that you will never
need a parking space again.

Softtop latches that lock.
Clutch slave cylinders that last 50,000 miles
Air conditioning that doesn't leak.
Premium sound systems that are actually premium.

There will be a blueish glow from the fusion reactor in the front, evident
through the grille.

The fusion engine will be driving the rear wheels through a four speed
transmission brought back by popular demand of drivers finding it difficult
to shift 51 times going from 0 to 100 in 1.5 seconds.

The wheel-thread surfaces will use nano-activators in them to establish and
reversibly peel away mechano-chemical bonds with a dry road surface, but
commercially viable systems can achieve no more that 7 to 9 g of mean
adhesion on a good surface.  Worse, on a wet surface, adhesion will plunge to a
precariously low 2 g or less, as the nano-activators are still limited in
creating the needed active-control micro-pressures and viscous shear stresses
to generate traction on submicron road roughness passing by at 1500-2000 mph.
It is expected to take at least 3 to 5 more years before in-thread processors
reach the computational speed to pro-actively resolve every submicron roughness
feature, rather than sampling them statistically.  Until then, the Miata speed
limiter will activate at subsonic speeds on wet roads.

Needless to say, the thread is magnetically suspended using superconducting
magnets.  Classical "tires" are still allowed at nostalgic events, when
conducted on bicycle paths, but just image a sidewall rolling over when you
are trying to take a sharp curve at, say, Mach 1.5.

A protective shroud will automatically be raised when you reach transonic
speeds on the Intersonics, since the greater air penetration into the cabin
may yank off your oxygen mask.  This is another good reason for Miatas to
stay off the Intersonics and leave them to SUV drivers.  As is the fact
that a SUV which is aerodynamically lifted off the road because of its
excessive frontal area may come crashing back down on a Miata.

And you don't need the Intersonics anyway, since Miatas come (optionally)
with a teleportation device to transport the Miata instantaneously from
the end of a mountain pass to the start of the next mountain pass.

Of course, all Miatas come for safety reasons with a heads-up, through-mountain
display.  Note however that this is not really X-ray vision through the mountain
as many unsophisticated people believe.  The info of what is beyond the curve
comes from satellite data superimposed by the windscreen on the image of the
mountain side.  Since the total amount of info that can be pushed out of
satellites is severely limited, a well known problem, the info of the other side
of the mountain wall will have been buffered and may be microseconds out of
date. And it will have been severely compressed, making it hard to distinguish
between a deadly 18-wheeler, a nasty motorcycle, or a harmless pedestrian.
The driver should probably assume the worst.

There is a cheat mode to warn of gravel or sand in the middle of the curve,
but this is not considered fair play by Miata aficionados.  Also the satellite
data at that level of detail are likely to be hours out of date; the gravel
may well be gone by the time you get there.

All Miatas come with an antigrav button for when the driver comes in too hot
into that mountain hairpin.  But the energy requirements for anti-grav are
astronomical, and the Miata driver has only a few milliseconds to decide
whether he wants to spend the rest of his life as a miserable pauper or just
end it all right now.

Renegade satellites operated by China are programmed to recognized US police
cars
and give proximity warnings, but possession of receivers for those satellites
is illegal in most states.  Also, most police cars jam these signals; however,
it is legal to detect this *jamming* of signals, and most Miata owners use it to
detect the proximity of police patrols.

At constant dollars, the Miata would be much cheaper than 80 years ago, when it
was first introduced, except for the magnetic levitation devices required to
provide a virtual shelf for holding cups anywhere along the length of the
dashboard. Do not drop a screwdriver on the virtual shelf, though, since
the magnetic field may pull the shift and manual brake handle sharply forwards
and upwards. Accidents caused by this abuse are not covered by warranty.

Miatas will still come in many colors, but there will be a polluter-fee for
nonwhite Miatas, as the additional energy required to make them keep up
with other traffic adds significant greenhouse gases to the atmosphere.
Adding a lot of chrome to your white Miata is a further way you can be
environmentally friendly.

Leon

The 2070 MX-5 will get 60 mpg.  It will have LED lights.  It will
unfortunatley weigh 2600 lbs. but horsepower will be just over 200.
Otherwise will will be exactly the same.  Oh yeah... and it will be
offered in Red, White, and some form of Blue.

Jeff

Maybe they'll have gone back to pop-up lights, albeit made of some
pedestrian-friendly plastic.  What goes around comes around.

I think we'll see a longer hood, ala the E series Jag roadsters, to
accommodate the extra room needed for the hydrogen extraction unit
(which will feed the fusion based power plant).