With the latest release of NVIDIA's Drivers, CUDA can use PhysX(and the FPS is amazing, in the Game to test it, when I had 8-20FPS before, I now have 50-60FPS almost constantly)
Since most people own a NVIDIA card, I think it'd be great, maybe in M&B 2, cause I think it can't be put into this one(Engine Limitations), if you included PhysX and you could use Siege weapons to actually rip apart parts of the castle with Siege Weapons...that'd look so epic, you'd see a part of the wall fall, and the men on it screaming as they're crushed and whatnot, and the one guy who was ontop of them all, and is still alive, and goes F**K when he looks at your archers.
Just an idea, Havok was good, but PhysX Physics seem to just be the best ever, currently, that is(Of course, you could disable or enable it, like some games do) It'll probably replace Havok, as I think ATi is even going to support it(I read about how they were working on Havok on theirs, but dropped it, it appears most people now see PhysX as the top, so probably in 2-3 years, most cards will have a way to enable it, and you won't need a PPU)