Well, let's considere how the Balkan situation might have developed. South Slavs are basically defined as Croats, Bosniaks, Serbs, Slovenes, Montengrins, and Bulgarians. Out of them, Bosniak and Montenegrin might never have developed in this timeline since their branching off was mostly due to Ottoman influence and who knows how that went. A Croat or Slovene national identity might not exist either considering where the Ilyanens are located- they are probably subsumed into the Ilyanens or the Serbs , since it's doubtful that a minority rule or a multi-ethnic state could exist within that tiny piece of land and still manage to go around and form a global empire. (If not so, such a state would've exploded into pieces during or after WWI like the Russian Empire or A-H, since they were on the losing side I believe). There's always the possibility that they are minorities living in Bosnia though, I guess?
For the rest, Albanians are also taken into question since while their origins are disputed, the most-widely held view is that they were derived from a small group of people who managed to expand rapidly during the last few centuries. (There are also the theories that they are descended from Dacians or Illyrians, but they face problems, such as inconsistency with genetics). AKA they might not exist either.
No problems with the Greeks though. They've been around forever.
That being said, what are the Ilyanen anyway? Are they Christian? Muslim? Are they of Slavic descent, or of some other ethnicity? (Or at least what ethnicity do they consider themselves as?) Language and alphabet? (For example, do they use the latin alphabet?)
Regardless, there is a lot of room to work here in the Balkans, especially since the Ottomans don't seem to have had as much influence in the area, judging by the existence of a Ilyanen state and how prosperous it has become, and considering that the Ottomans have been effectively ruling the area for centuries... that's a big point of divergence there to make for many possibilities.
