At the dawn of the 14th century, the Byzantine Emperor hired the Catalan Company (1,500 knights, 4,000 almoghavars) as mercenaries. In Anatolia they defeated the Turks and added some Horse Archers in their ranks. They weren't shy about pillaging the Byzzies as well, but it didn't seem any of the Turkish factions of the day could stop them. Their leader, Roger de Flor was suspected of wanting to set up his own principality in Anatolia. In the end, the emperors betrayed them and massacred them using the Alans and they ran around causing chaos on the European side of the empire before being hired out by the Latins of Athens who also betrayed them. The Company ended up conquering Athens and the Morea and ruled it for 70 years.
So the WI: What If the Byzantine Emperor supports Roger de Flor's setting up a state between the Byzantine and Turkish areas incorporating parts of both? Will they attack the Byzantines? Will they attack the Turks? If they are a buffer state for 70 years in the east, how does this effect the Byzantine Empire?