The PC world has already switched architectures 32 bit to 64 bit already so its doable. The big issue I think is if you are Intel / AMD why would you do this?

The PC world has already switched architectures 32 bit to 64 bit already so its doable. The big issue I think is if you are Intel / AMD why would you do this? Even if there are performance gains do you really want to undermine one of the things (backwards compatibility) that distinguishes you from the competition? Plus what would the new ISA be? Plus Intel still has the memory of Itanium.