The changes with 3.1 won't make much of a difference most likely. There's also no switch flipping to increase performance. Cider ports will always have noticeably lower performance because of the emulation going on. To use the Metal API, they'll have to code a native client from scratch. Better option would be to go for a native OpenGL client (considering the PS3 uses a customised version of OpenGL, they should be able to use code from that client), but Square claims a native OpenGL client doesn't perform better than a Cider port.

In the end, there are just not enough Mac users (who don't run Bootcamp) to warrant doing a native Mac client.