Dear Jeff,
My 2 centicredits ...
You could (if you wanted) realistically portray the Mmarislusant as hyper-traditionalist, glomming on to obscure and never terribly prevalent Vilani traditions, then turning those traditions up to 11. Thus they can distinguish themselves from the majority Luriani culture.
In the Australian context, it is widely recognised that the large Greek-Australian community define themselves using a set of cultural practices that bear little or no relationship to contemporary life in Greece. Instead, it is an ossified and exaggerated version of what Greek culture might have looked like in the late 1800's.
Similarly, consider the factors and practices that have continued to define "Jewishness" despite prolonged exposure to a majority culture.
From a gaming POV, there is potential comedy value in having a Mmarislusant, an inhabitant of Vanejin, and an office holder in the Restored Ziru Sirka bickering over what makes a "true" Vilani.
And I have mentioned, many years ago, that I don't see the pre-Ziru Sirka Vilani as being particularly conservative or reactionary. No more so than the Romans, anyway.