Agreed, I do think MPE is the future. I think it'd be more likely that Ableton would have a secondary controller for MPE than take Push and give it a continuous (for want of a better word) surface like seen on the Linnstrument. What you might see is some sort of MPE hybrd functionality in a Push 3. No ability to slide between notes (the gaps would remain) but vibrato, lift, attack sort of variations could be possible on each of the 64 pads.
But it all goes back to my original point - the market for MPE is still tiny. Ableton could be the guys to crack it but it'd quite the gamble to go all in with software and hardware for the next iteration.