From the steam forums:

 [developer] Feb 6 @ 11:36am 

well I guess that is that.

Since I have no desire to play the new game, I suppose my time here will be more or less non existant for the next few years.

It was nice having you around! Just keep in mind that what they are saying is that they are not currently in the middle of making a new expansion, but that they aren't closed off to the idea of making additional DLC after Humankind is released (though they can't promise anything either). Hopefully I'll see you around!