I've ben told that:
64-bit Maya is coming but 64-bit Cocoa Qt libraries for OS X just came out. You'll see Mudbox, Maya, Maxwell, Realflow, etc release 64-bit OS X versions over the next while. The 8 cores isn't related to 64-bit - that's simply a licensing problem with Mental Ray. Maxwell Render, VRay for Cinema 4D, etc all use the eight cores.