by fizolof
The easiest thing I can think of are new races - sheet, cards, tokens - nothing needs to remain hidden so there'll be no problem with slightly different PoD painting.Another cool thing could be new systems (tiles and cards), though the tiles should be similar to the existing ones OR they can add a whole new scenario with a fixed map setup. And then the possibilities are infinite - even the core mechanics can be changed.
PoD with an alternative Strategy Card(s) would offer a twist.
One more idea, maybe not necessarily new plastic units (high cost), but unit-token can be attached in PoD. I'm thinking an upgrade versions of existing ones, like they did with ground forces and veterans. Fighter squadron leaders?
Oh, something which may call for a large expansion: culture, like in Civilization games. TI covers military, political, science, economic, trade agendas. Why not add culture? Oh, or advanced espionage? It would require some major changes to races, techs, action cards etc. and would rise the difficulty level over the ceiling, but TI would become even more epic!