The issue I see with this is that while the suggestion for a family-based game would be close to CK2 this lies very close to V2 as that game has various competing factions that you try to keep from tearing the country appart and still go forward, even if economics is the main "thing" of that game.
And to be honst, if we are playing a country then what harm, aside from our pride, is there in letting an ambitious general do his coup and take over? We still keep control over the country and can easily engineer another general to conduct a coup if the first general bring unwanted changes. Just like we can in V2 simply move armies out of the rebels' path and let desirable rebels take over the country if we so want. Thus the whole part of rebellious generals becomes either at worst a speed bumb or nothing to worry about as far as the gaming aspect is concerned as it don't interfere more with our plans than we want it to do.
Really depends on how they ectually implement a civil war. In my mind it should be less about EU-style rebels and more about your empire splitting apeart in 2 factions and you have to defeat the other one. Cheesing out by choosing one site and let the other just win can easily be negated by making you go gameover when your side of a civil war looses.
On top of that there can be multiple nasty things get included that make sure that if you let it come to a civil war it's not gonna be just a matter of another general getting in charge, because it sets you back 50 years in your imperial march towards world domination: Decades of unrest and prosecutions in the aristocracy after the war (like after Sulla), they can implement that a year into the civil war some recently conquored area will go full rebel and declare independency (perhaps even allied to the other side of the civil war). Devestation throughout your empire should cost you lots of time, money and mana (if around) to restore just like after Ceasar's civil war the eastern provinces where virtually depleted of anything of value. It's just a matter of how they implement it but I really don't see how a system where you feel like 'herding a bunch of plotting, backstabbing, machiavellan cats' would inherrently lead to civil wars being just a speed bump, there are plenty of ways to make them really impactfull.
I can't say I know Victoria 3 well enough to argue about this looking too much like the internal politics over there but as far as I know there isn't anything like the Roman Senate system from EU:Rome there right? with characters with family ties vying for positions in the government etc.? it seems a bit far fetched to compare these things one on one since it's not just a few pie charts with factions and pop's but more about real characters making the factions. Seems like a totally different thing that would really nicely fit right between the character based gameplay of CK2 and the Empire level gameplay of Victoria and EU.
Pops is pretty much a fan favourite from the community but I feel they should leave that for Victoria, Culturals diversity in provinces should totally be a thing though considering this was quit important in how much manpower there was available for legions or greek phallanxes and how much for auxillary units.