Anyone tried this combo yet? Tried searching and it hasn't come up.

2011 Red shifter users say the yaw FD works great, and previously the 7800 FD was the go-to derailleur, so its only logical that it should work, right?

I figure for the price of buying a 7900 FD plus a chain catcher, I might as well just get the whole unit and get some yaw action with it.

probs not.

7900 is still better. and the new sram derailleur isn't designed to work with a trim position (hence the sort-of-incompatibility with old red). I'd just stick with a complete group, as front shifting isn't a problem with 7900, in fact it is one of the group's best features.

7900 does not trim either.
But I would stick to the 7900 front derailleur too. Buy the Red chain catcher separate if you like. IMO the yaw FD is not "the dog's danglies", setup is a lot more finicky. The line between rubbing in the hardest gear and throwing it off the big ring when shifting is much tighter.