yoooo that idea is crazy good!!!!
1000% agree. I like transitions, they're exciting - but currently only after the transition. It feels like, well, starting a new game, sort-of. I'm the classic player with more 50-turn antiquity saves that I never continued than I count.
But the end of an era can be total drag. I always hope for riots at the end of an era - trying to put out a negative happiness fire, settlement rebellions, a surprise war; when not everything is in my control is when I'm having the most fun in civ!
But sometimes the end of an era just isn't exciting. If I don't need to finish the tech or civics tree, why put a new district anywhere? I've got the army I need, why build military 8buildings? I'm past the settlement cap, do I really need to start making 200 clicks a turn for conquest?
New angry Independent Peoples is engaging, but not threatening enough. Not always enticing. If my towns furthest from my capital rebel, though, and they don't just change factions - they turn Independent and hostile, that sounds like fun! And rather more realistic for both ages.
And if I'm playing on Deity with, I dunno, an Age Crisis Difficulty slider turned up, and I can't recapture every settlement (and maybe I did manage to take a neighbors)... that leads to an exciting new start, truly. Now I'm free to settle more settlements in Distant Lands - and I'm even more incentivized and able to do so, too. If I'm a civ that can spawn treasure fleets in the homelands, there's now more options for me - and more of a reason for other civs to deny me those options.
And what a better way to make a new civ feel like, well, a new civ! Out with the old, literally, and in with the new aye?