Probably and old one, but…
When polishing an APP after initial minimal development (and changing language of some of the things left in a local language or vice versa), I find it cumbersome to delete and make new states for elements. Also, getting an overview of the states in an app, would be a quick way to see what data goes where.
I would really like to see a small box with a list, or even better, displaying states next to elements in the elements tree (toggling the list on and off, just like the hidden elements tick box).
Small but really useful feature, with minimal impact on the UI.