My interest comes from that I am starting to look over at reading more about Rome due to the fact that my brothers are interested in Rome and I like discussing history with them.
To that also comes that I want to make my opinion known in this issue and since I am entering a Crusader Kings 2 phase in my life, from previously having played mostly Imperator, I've started to hang out more on the CK2 subforums. And from there I noticed this thread.
Cultures in CK2 don't need to be perfect replicas of their real life counterparts. But it's not like we routinely see Frankish dukes riding war elephants and women becoming Pope. When that happens, it's a funny surprise. So why should (barring Shattered World of course) CK2 Romans be unrecognizable from the Romans of Antiquity? I mean sure restoring the unified Roman empire is already alt-history but CK2 doesn't have two Roman cultures (one for Roman emperors of Antiquity and one for the reformed Roman empire) either. The Roman culture IS the culture of old Roman emperors of Antiquity, who did not routinely blind and castrate their enemies (but often asked them to perform suicide, something not possible in CK2).
Besides, adopting Roman culture is a choice. It's okay to have a trade off on a choice. You can restore the Roman empire and retain the Byzantine culture. You already "won" CK2 by restoring the Roman empire.
You are right in that cultures don't need to be perfect replicas, but they should in my opinion be reasonable simplifications. But I don't think that this is where our main point of divergence is.
What I think is that its rather clear that we are not playing Classical Romans, we are playing neo-Romans who, from very sketchy foundations given the absence of archeology and modern intellectual tools for analyzing the texts, have reinvinted themselves as Romans. These are neo-Romans. Short and simple and I see no way around this.
To this also comes that "Roman culture" before the West fell lasted for some thousand years or so. Probably more. And from this I think that its ludicrious to try and define one set of Roman values or cultural traits in an absolute way. It just morphed and changed across the centuries too much. Early and Middle Republican Romans probably wouldn't see much similarities with Diocletian and his introduction of the Dominate. But they were still all Romans. Nor did the Romans ever practice feudalism but to my knowledge its perfectly possible to do so in CK2 with Roman culture.
In fact if Paradox ever does this thing in CK3 I would advice that we can pick one of three different types of Roman culture to re-create; Republican, Principate or Dominate. And perhaps even more choices to pick exactly which ancient Rome we're trying to recreate instead of taking bits and pieces all over the place and try and force an egg through a square hole. Yes, it can be good for a casual play through but anything more and its going to fall to bits, at least in my eyes. As I think our discussion here hints at.