Star Citizen is weird. If you have Nvidia, you are going to have PhysX true.
But if you have AMD you get True Audio, Mantle, TressFX and Eyefinity 2 etc on that game though.
As for Mantle, is out what 4 months now? 2 games support it already.
15 games are coming soon using the Frostbite 3 engine and going to support it also.
In addition we have Beyond Earth announced to do so, Star Citizen and couple others.
And is retrofitted to almost every big engine out there. CryEngine, Unreal Engine, Frostbite 3, and is included on Oxide's Engine.
I bet by end 2015 we are going to have as many Mantle titles, as we have with PhysX over the last 7 years.
Which are less than 30 according to Nvidia, minus one that has it officially off (Planetside 2).
TressFX runs on either Vender iirc
I dont see mantle being retro fitted to any existing games even though a few could make good use of it