Looks like you've been flailing along quite nicely (flailing = waving
arms and throwing parts at the car in the hope that this will fix it.
Eventually - if you replace the entire car - it will, and of course the
last thing you replace will be the problem component.)

The ignition relay is certainly a failure point - and not horribly
expensive to replace if you're going to flail. I'd prefer to check the
output of it with a voltmeter before spending the money, but if
diagnostics aren't your thing and your wallet is deep.. go for it.

The ignition switch is an unlikely point of failure IMHO.

I also experienced a failure of the Motronic in my old '87. They have a
failure that isn't uncommon of the solder joints in them that eventually
failing due to heat cycling. It's usually one of the output transistor
joints. A used one off a wreck fixed mine, then I disassembled and
resoldered ALL the joints in the old Motronic - and tried it in the car.
It worked fine after this.

If you loose all spark - it is very unlikely to be plugs, or plug
wires, or cap. These might cause loss of spark at one or more plugs -
but not all 6. Total loss could be rotor, might be coil - but all of
these are simple to check with an inductive timing light (or a simple
neon ignition tester) - saving you a whole bunch'a money.. but like I
said, if diagnostics aren't your thing - dig deep and often, the
dealer's parts department will become your friend.

You have electrons at the battery, jah? Where do they stop exactly?

When my 635 did this is was a bad connection to the Motronic TDC sensor
on the bell housing.