Spliscreen really is a make or break Crysis to me, at least for 360.
If they add it, I'll buy it since I can play with my freinds/girlfriend, if they don't er'll just stick to the games that support it, like Borderlands, Halo, CoD, the list goes on.
Split screen on consoles are at least as important as dedicated servers and modtools on PC.
Sure, graphics would be worse but that wouldn't really matter