[Q]

Many of the interesting things proposed here need a hard-code change, but we have quite a few possibilities to keep the game interesting when your empire has reached MEE status and you actually have won the game (many of these ideas have already been mentioned on other threads):

1.) Switch you empire to computer contol and choose a small empire to continue the game: There has been a revolution and you have been exiled!
2.) Make a gift of as many systems/colonies/ships/technologies as you want to a computer empire (you may have to take control for one turn over that empire to make sure that the gift is accepted): This would correspond to the civil war/rebellion.
3.) Switch all computer empires to manual for one turn and make them surrender to one AI empire you think is the most dangerous: All other empires form a strong alliance to combat your empire.
I did this once with my Borg assimilation modification race and was quite in trouble!

Of course nothing of this is random, but you can do it right now without any modification of the game.