A Brief History of Albania during the High Middle Ages
as written by a Certified Fourth Grader*
~880 AD: Conquered by the First Bulgarian Empire.
~1014 AD: Conquered by the Byzantine Empire.
~1081 AD: Raided by the Normans of Sicily.
~1190 AD: Conquered (partly) by the emergent Serbian Kingdom. The first independent Albanian principality is established.
~1204/16 AD: The Fourth Crusade leaves Albania under the dominion of the Despotate of Epirus.
~1267 AD: The Angevin Kingdom of Naples conquers Epirus (and thus Albania), King Charles d'Anjou styles himself »Rex Albaniae«.
~1281 AD: Byzantine reconquest of Epirus.
~1343 AD: Stefan III Dušan, Tsar of Serbia, conquers Albania.
~1355 AD: Multiple Albanian princes regain their independence. Around this time, the distinctive Albanian culture starts to emerge primarily in the Kosovo, Epirus and parts of Thessaly.
~1392 AD: The Republic of Venice conquers most of the principalities, actively engaging in regional politics.
~1430 AD: Ioannína falls to the Ottomans.
~1443 AD: Skanderbeg, valiant prince of Kruja, founder of the League of Lezhë, defends his people against the Ottomans for nearly a quarter of a century, holding out in Northern Albania.
That's not an awful lot, but I can definitely see how crucial Albania's role was in the final hours of Byzantium. It seems to have been a trading hub of moderate regional importance, especially Durrës/Durrazzo/Dyrrachion; the problem with implementing the Albanian culture is probably that it would be restricted to a single county for almost the entire period of the game. I must agree with you, however, that there's a severe lack of Balkan characters in the game (I've never once seen Bulgaria formed by Bulgarians, and Serbia likewise never by Serbians), and in the Byzantine Empire especially.