Given that the POD must be after the Greek War of Independence, how far can the Greek nation stretch out by 2000? Can the Hellenic Republic control Macedonia, Epirus, Thrace, Pontus and a good chunk of Anatolia without turning into a military dictatorship?
(Planning stages for my first TL, which I bet will not be about Greeks nor about highly improbable situations)
Well, to start with, accomplishing the Megali Idea is pretty implausible. I believe it started off as being replacing the Ottoman Empire with a Byzantine one, which was pretty crazy anyway and is ruled out by your PoD... and then as to "uniting all Greeks in one state"...
Well, Cyprus and Southern Epirus ought not to be hard, and Imbros and Tenedos aren't so tricky to hold down. Constantinople is most unlikely since this required totally breaking the Ottomans and the most likely candidate to be able to do that, Russia, will take "Tsargrad" for itself. Anatolia, too, woud require the Ottomans to be broken.
One could get a differant border in Thrace somehow, I should think. Macedonia is an interesting question, but I think there is probably some scenario in which Vardar and Pirin Macedonia can be acquired.