CPU arch. would be the least of the problems. They can do roughly the same trick they did with the PowerPC -> Intel switch years back. The problem is that you

CPU arch. would be the least of the problems. They can do roughly the same trick they did with the PowerPC -> Intel switch years back. The problem is that you cannot just put a keyboard/mouse centric on a touch device. The entire UX will crumble down. Same story the other way around. Small things like buttons and textfields need to be bigger and more spaced out. Entire panels need to be redesigned as the control density is lower. To get the same quality of UX you need to design for both interface methods. iOS suffers the same when attaching a keyboard to an iPad. A lot of small things like workflow shortcuts and navigating the control space with just a keyboard just don't work (yet). Forcing you in either a touch-only mode or having to switch between keyboard and touch constantly.