. . . The challenge is going to be that a lot of modern European nations are going to go through the Romans, but only one player per game can take the Romans. No problem in single player, I suppose, although I can see someone who wants to play an historical chain being peeved if an AI selects one of the links in their chain.
You're right, though, that the European nations that arose during era 4 (called different things in different articles, including Renaissance and Enlightenment and Early Modern) aren't all going to fit in a 10 civ slot. We might see French-, German-, and English-chains, with the rest of Europe left for DLCs.
I do not see how they can even begin to satisfy everybody with only 10 Civilization/Culture Groups per Era when there are 'Bottleneck' Eras such as the 4th/Renaissance/Enlightenment. Especially since there are also Civs that although they have existed since Medieval/Renaissance Eras had their 'Peak' in those Eras, so they place even more pressure on the Bottleneck.
I suspect, in fact, that it is going to be very difficult to arrange a 'historical' progression through the Eras. If France, in your example, could be Celts - Romans - Franks - France for a 'historical' progression, then Romans could also be in the progression for Italy, Romania, Byzantium, and England/Britain, at least.
There is also the 'problem' of Civs that are amalgamations of several earlier Same-Era 'Civs', like Byzantium (Greece/Rome, both Classical) and France (Celts/Rome, also both Classical). Given their current Model (or at least, what we know of it) they might wind up with some 'floating' attributes that can be selected in an Era to 'customize' your progression, so that a progression that should include 'Rome' can instead get by with a Roman-Like attribute or 'Unique' instead.
In the Far East, the Chinese influence could also cause problems for other Civs as different as Japan, Korea and Vietnam, all of which were heavily influenced by various Dynasties/versions of China. IF the influence is limited to one Previous Era Civ per Civ, I can't see how to avoid some major disconnects.
That may, in fact, be one reason why 'staying the course' and not changing from one Civ to another through the Eras is being made an Attractive Option: for some Civs, it may almost be a requirement to come even close to an 'historic' progression, for those interested in playing that way.
On the other hand, someone correct me if I missed any mention of it, but such 'variations' in progression open up a wide highway for Alternate History: a France that never had a Roman (or Celtic) Influence, for instance, or a Korea with no Chinese Influence, an Egypt without any input from a Greek/Macedonian Dynasty or Nubian Dynasty or a China whose Dynasties have no 'northern Barbarian' influences - which was most of them!