YES, this would be brilliant, the icing on the cake making the late-game stage much more interesting.
I haven't read all of the suggestions, so forgive any repeating here. Perhaps the following could work:
Exodus - An emopire suddenly suffers some disaster and must move on or die, their population being converted into loaded, long range, troop transport ships, except for, say, their most recent colony (if planets are a requirement/there aren't any stations).
Religious/Idealogical movement - A new Civilisation is generated, gaining a percentage of all the races planets and ships.
Pan-galactic fertility - all/percentage of class 0 planets become habitable (random generated class perhaps).
Enlightenment - by fortunate coincidence, one empire is now home to a load of home-grown geniuses, doubling their research rate.
Hyperspace... or something-space anyway... - For a limited number of weeks, all ships have either/both vastly improved speed or no limit on range.
Anyway, at least the Exodus thing is an event I've always wanted to happen to me

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