I'm guessing people will always make that last-minute-push for the extra planets at the last turn(s). The thought crossed my mind that not having a set end turn but rather a cumulative probability that the game will end on any given turn would be interesting - e.g. 2% chance of it ending on turn 150, increasing by 2% each turn until the game actually ends.
Not really supported by our current system but I thought I'd throw the idea out there.
Show Media Item - most planets at turn 175 is much too long for this game...