Interesting; it's always fun to see how other GMs make campaigns in the same setting. (I've never checked into this for any other game I've run, so doing this for Numenera is new for me...)

In addition to what I posted on the google+ page (as Josh MacLeod there), I actually think the aliens arriving back on Earth WOULD be fun. Not as an invasion, per se, but a holiday to check out the famous centre of the Trans Galactic Hub and finding out everyone is living as barbarians would be great culture shock, and perhaps highlight to PCs a hint of how much as been lost -- or was taken away -- from humanity.