I'm assuming this is going to be implemented at some stage, but I think there should be an option to have different players (human or AI) with their initial spawn on different planets. It would be awesome.
They are probably waiting for orbital invasions to be viable. At them moment, when one player completely holds one planet and the other player holds the other planet, it's neigh impossible to invade. Just pump out T2 bombers and put them on planet patrol, liberally sprinkle ion cannons and antinukes around (which is no problem with a planet worth of eco) and you have an impregnable planet.
I would expect to see multi-planet starts once we have the ability to move moons and asteroids into orbit. There is still a lot more work to be done related to invading planets, but there is no reason to finish all of that first.
Yup that hit's the problem spot on. I think it has been said that once that's done, starting on different planets will not take long to be implemented.