I'm also deeply skeptical of it possibly be a good mechanic, but the one way I can see where it might work is if you don't actually get to choose how your civ evolves and the game chooses for you depending on how you play. eg You become the Mongols by being a mounted warmonger, and you become the Mughals by making a lot of money. I don't think this would actually be good because specific players would end up being the exact same civ game after game unless they specifically try to do different things and it'd do bad things to the meta, but at least it's not what we saw with Humankind where there's like 2 to 3 civs worth anything every era that you pick every single game.
I would also hate it less if it's deeply historical and you really just have a few civ "paths". I think that'd be inferior to just having civs, but at least I wouldn't always just be jamming whatever gets me the most science.
The part that I'm still uncertain about is how much option you'll have for the civ choices in those eras. Like so far they've shown the screen where it seems to imply you might have like 2-3 choices on the age transition. I think if they can find a reliable and balanced way to give you an option like that, that might be good. Basically, you can go the historical route, but if you've played the last era like a specific civ, then you can "develop" into them the next era.
I don't really want you to be able to get to the next era and go to like the civ picker screen where you get like 10 or 12 options available to you. It would feel weird to see you make 3 fishing boats and suddenly be able to turn into the Majapahit empire. I kind of wish that maybe in the crisis period, you would get like multiple quests to unlock the next civ you might be interested to develop into. Like maybe every next era civ would have like an initial trigger condition (so Mongolia would be the 3 horse resources), but then when you hit the crisis, you would have like another quest to be able to actually unlock them. Maybe it would be to build 6 horsemen and capture a city with those units. The Majapahit would unlock with 3 fish resources, but then to actually be able to transition to them you need to buy 4 galleys and settle a new city on a new island. Although if each civ only had one option there, I guess that just turns into a longer chain to unlock. So maybe I just want each civ unlock to be at a relatively higher threshold than what we've seen so far.
Something I think so that you get like 3-4 options at most for who to potentially develop into. But I do like the idea more along the lines of "if you played the last age like a civ, you can become them in the next era." If you spend the first era pillaging from the sea, then it's only natural that you could develop into the Vikings for the next era.