First of all? Oh my god, the fanservice. Hahaha.
Okay, now on to the meaty bits: These are the portraits I spotted in the end which I suspect denote who's playable:
Arthas (Pre-Lich King) (Lothar, maybe?)
Arthas (Lich King)
Muradin Bronzebeard? (Dwarf-on-a-Gryphon)
Abomination(Maybe the Butcher?)