Per Page 23 of the rulebook (just posted today July 30): Five expansions are already planned, the first to bring artillery robots into the game;
the second a full-blown two-army set that takes place at a German castle and introduces strange Axis creatures and adds new tiles;
the third intros faster and more lethal robots as the timeline progresses, as well as a new generation of soldiers and new heroes;
the fourth expansion intros the Vrills, an alien race, and includes an army of models for them and more terrain tiles;
and the fifth adds air units to the game.
Sounds awesome and expensive at the same time!