Not to sound like a jerk, but is that actually what you think? Answering every question about a character is not the same as a fully developed character.
This episode was all about Marc's story and how Steven came to exist, which was the main plotline for this whole series thus far and what we've been building towards.
They've definitely hinted at a third alter, but we still have an episode to go, which will probably be a long one. But that won't really change that the story was about Marc.
At this point I feel like the third one will just be an embodiment of Konshu rather than a whole other alter whose backstory we've yet to see.
This episode was all about Marc's story and how Steven came to exist, which was the main plotline for this whole series thus far and what we've been building towards.
They've definitely hinted at a third alter, but we still have an episode to go, which will probably be a long one. But that won't really change that the story was about Marc.
At this point I feel like the third one will just be an embodiment of Konshu rather than a whole other alter whose backstory we've yet to see.