It's certainly possible I think, but what you're talking about is more-or-less asymmetric multiprocessing, which (according to Wikipedia at least) is generally more complicated to implement at a hardware level:
Exactly, this is just an asymmetric MP configuration. Note that this isn't exactly groundbreaking either. Others have already been using QPI to hook FPGAs up as accelerators. I don't doubt that it's a complicated technical endeavour, but Apple is certainly home to a number of talented engineers:
http://www.nallatech.com/Latest-News/xilinx-demonstrates-int...
http://www.eetimes.com/electronics-news/4207772/Xilinx-demos...