Space Empires IV Risk!

[Nocturnal]

My first reaction was, "Won't this take like ten million years?" But if you make the combats tiny-galaxy games, like a handful of stars, then perhaps it will be possible. I think it can be decided by a single battle: give people the same starting conditions suitable for a very short game (plus modifiers for fleets used,) and have them use the first 20 turns to build up, and on turn 21, duke it out with whatever fleets they've amassed by then in a predesignated system. This slightly favors one style of play (for example, nobody is likely to invest race points in trade or maintenance) but should hopefully still allow some diversity in tactics.

Ties in well with the custom maps that are required to simulate "terrain." I can see it working with as few as 3 planet-rich systems: one for each player, and one for the battlefield.
You can maybe make an event which will open a warp point between the systems?

Still, I think if many combats happen each turn, it may take several hundred thousand years to get through a game like this.