REX is horrible because they occupy two full rows of what were otherwise very useful instructions (inc/dec), and there were other gaps and less-useful instructi

REX is horrible because they occupy two full rows of what were otherwise very useful instructions (inc/dec), and there were other gaps and less-useful instructions (segment override prefixes? If segmentation doesn't work in AMD64 mode, what's the point?) in the opcode map they could've used instead.