The bigger barrier to TSL is the map expansion, which with the info we got it may be able to be implemented on single player and mp with some restrictions, of only picking the ancient civs of one half of the map, and maybe later after some patches expanded if they make it so you can mp both sides of the map at the same time.
The civilization switching is less of a barrier and more something that would make it a different type of TSL than other games, which may be good for some and bad for others. If you play TSL because you want to eventually have a terra map with almost all civs at same tech level around where they would be, then it won't be able to do it well or at all. If you want to play it because you want a true historic like TSL experience, then it will make it even more like it with the limitation of the civs from the particular age. After all, for example, America didn't start in the america continent, but ninstead it was people who came from a different place, established a colony there which then gained independence.
I've seen that being said around but so far seems like a misinformation or at least exagerrated, maybe because the age of Exploration follows Antiquity made some people think it will skip all the way to 1400 or something?
As far as we know, the time break between ages would likely be the amount of years of 1/2 turns break time for that point in the game.