It's why FO:E ended the way it did, actually.. so Kkat could return to the 'verse at a later time, if so desired. That likely won't happen anytime soon, and if it does, it'd be more like a side-story about characters besides Littlepip; I mean, how are you supposed to top the existing story without venturing into Mary Sue territory, ya know?
Basically, the official answer is to not count on it happening, but not to bet against it ever happening either. The fandom is doing a fine job of creating a vision for the rest of the post-apocalyptic world as it is.