[Raapys]

It'd definitely work better with simultaneous movement, that's true. However, the best approach might be something similar to how Master of Orion 3, which also uses simultaneous movement, processes turns. It basically finishes all movements for all empires, then stores all potential combats.

This way the game could just go ahead and process all empires' movements at once, using all the cores. When that was finished, it could then go ahead and split the combats between the different cores. This way, the only thing that would have to wait would be those combats dependant on the results of previous combats the same turn.