I won't believe any info regarding compatibility until someone actually TRIES it.
We just (finally) got the stuff in-house, I'll be trying old shifters/new FD, new shifters/old FD combos today. Already tried new shifters, new FD and old crankset/rings, which works better than old FD/old rings, but not as good as going with the whole New Red system. Probably 80-90% as well. Without trim and with the slightly different ring spacing, you get slight chain rub in 39/11. But who rides around in their 39/11?
I've been told by a "knowledgeable engineer"
that the FD cable pull is the same, it's just that the 2012 eliminated the "trim" spots, so it's very possible to run the 2012 FD with older SRAM shifters.
Also, although the spacing between the teeth on the rings is wider, that's all done in the rings (i.e. the thickness of the ring mounting tabs is the same as previous cranksets) which means that the 2012 rings should be able to be mounted on other cranksets, the only issue being that the "drop pin" won't be inline with the crankarm since the 2012 Red mounting hole pattern is rotated 180 deg. relative to the pin (and the shifting ramps, of course).
Of course, on the "flip side", this also means that you can run the 2012 Red crankset (including the Quarq S975) using older rings and older shifters together. This might be an option for some who may want to "upgrade" to the new Quarq without having to spring for the 2012 Red gruppo. Again, the only real "downside" is that the chain "drop pin" isn't in the right spot...not that huge of a deal IMHO.
So...my take on the whole thing is that if you want to run the 2012 front derailleur, you should run the 2012 Red rings with it as well. Other than that, the choice of crank, year of SRAM shifter, etc., is all up to the user. You'll get the vast majority of the FD performance just keeping the FD and rings together as a "matched set".
For some reason, I have a feeling that sometime in the future we may be seeing versions of the 2012 "yaw" derailleur packaged with rings intended to retrofit onto older cranksets (i.e. the mounting hole locations, and thus the drop pin in the correct spot relative to the crankarm)...but, perhaps that's just wishful thinking on my part