Considering how long since last update, I very much doubt we gonna see more from this game. :(
But yeah it is kinda sad to only have a single resistance type in the game, as it pretty much dictates a focus on only specific units (specifically, cannons + baloons, with a few catapults for "economy", is one of the best comboes I think), where with more resistance types, say a bio wall afterwards, all of a sudden the arrow launchers would be needed in probably a significant amount too, and builds would be become far more interesting and complex, in what type of units to use and how much of.