The #1 thing I'd like to see from the Moto X 2 would be better "Touchless Control" integration. To me, THAT is the killer app, and it needs to have a fuller feature set with more abilities. That isn't to say I'm disappointed with the X-- it's the only phone that can do what it does-- but if Moto wants to stay ahead of the curve, it has to improve dramatically.
A better camera would be nice, but not a deal-breaker for me. And I'm not really interested in having the "TouchWiz Experience" on my phone, so I don't need IR blasters, eye-scrolling, etc.
As long as Motorola bumps the specs to make the performance as smooth as it is for the Moto X, that will be fine as well (provided it's priced accordingly). I don't need 2K displays, and Snapdragon 1000, or whatever comes next. Just make it smooth.