Well, the real issue is that everybody's important to the history of their region. Are the Asenids important to the Balkans? Yes, critically so, just as are the Serbs and the Istrian/Dalmatian city-states... similarly, the Albanians are a pain in the Ottomans' side for years until they're gradually converted...
To answer your previous questions, though, no, Romania as such is inappropriate as an emerging faction. Though the Vlachs and Moldavians are around, the conception of government is different, and neither becomes anything we'd recognize as "Romania" within the medieval timeframe. (Sorry, but this is established. Even most of the Romanian scholars I know are quick to state this when the state isn't looking over their shoulders.) When it comes to "state formation," the medieval Vlachs are a lot closer to the Welsh or the Appalachian Scots-Irish in mentality than they are to your classic feudal ideal. It's a fascinating region that the TW series unfortunately is ill-equipped to represent.
So.... The Latin Empire *could* emerge, the Bulgarians and Serbs should DEFINITELY do so, and the Moldavians could pop up as a minor (unplayable) faction very late in the game, as could the Albanians, and rebellions in Wallachia should be common coin as the locals play off all the outside powers against each other. As you can guess from my conversation with Kavhan, the Vlachs, Cumans, and Bulgarians are all VERY cozy with each other (Kavhan, I agree with Vasary on this one), so you've at least got some potential for interesting unit rosters.
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