>>4
Increasing the pointer size to 64 bits doesn't magically make the encoding for the register-register instructions less dense. And speaking of registers, you know they added more of them, right?
If you are willing to abandon binary compatibility, something like the X32 ABI could make good headway on tablet size devices. There's really no need to maintain PC compatibility for devices like that, either - just boot straight to protected mode and all those awful problems (mostly) go away.
Phones are definitely a lost cause for Intel at this point though. The market has already decided on ARM and Intel is nowhere near good enough to justify developers recompiling all their applications.