I read a recent report that BMW will drop the high-revving engines
used in their M-cars and replace them with smaller, lower-revving
turbocharged motors.  The claim is that this is a more-efficient,
"greener" path to high performance.  Another claim is that peak HP may
suffer, but low- and mid-range torque will increase, resulting in
similar performance.

How would they separate the "standard" turbocharged cars, like the
335i, from the M-cars?

Personally, I would lament the loss of the high-revving engines.
Ironically, I do not really think that high rpm's are "the best way to
go" (as opposed to adding displacement).  However, the engineering
aspect of it appeals to me.  To me, there is something particularly
"bad" (in a good way) about a really hot I6, the epitome of which was
realized in the 3.8L I6 in the E34 M5, and the 3.2L in the E46 M3.

Only once did I see (and hear, up close) an E34 M5.  That thing was
f.cking badass, I'm telling you.