Geographically speaking Seulecids are practically a certainty, there has to be something between Parthia and the meditterranean. Still...no Egypt? Or are they just going to make a few independent cities instead of a playable faction? I can't imagine that they'd make a Rome game where you can't recreate the extent of the historical Roman empire, so they have to be on the map for sure.
There's also the possibility that they will simulate Seulecid empire disentegrating by having them be just a series of independents, and Egypt will be a playable faction. It seems the map isnt going to go very far to the east. Opens up the possibilities for future DLC's too. The more they open the map to the east the more factions can be included, Seulecids being the most obvious, possibly Saka, Bactria and even an Indian faction.