it's emerged from the discussions over on the MOUL forums, now that they've actually got going, that I'm not the only one who felt that Cyan had fallen away from the guiding principle that they had followed from the earliest times, that (as Rand said in one of the making-ofs): "story is core." It's arguable that the multiplayer nature of the game made this principle difficult to follow, but I don't believe it made it impossible. All the Ages we saw would have benefited immeasurably from a deeper and more emotionally involving back story, and as for the main storyline of "season" one, well, let's not go into that again.
It may be understandable that Cyan had to concentrate on the minutiae of designing and coding to keep to the schedule they had set themselves, and it may be that they were saving the good story for a second "season" that they couldn't be sure was going to happen. But we have no such excuses. If we are going to make a success of any venture of this kind, either within the framework of Uru or outside it, it is vitally necessary that we go back to first principles and start from a story. Build the world and the gameplay and the puzzles around the story, keep the story at the heart of whatever we do, and I think whatever we do will have a fair chance of working. Ignore or skimp on story, leave it till the last while we concentrate on getting the texture of the trees right and the widgets working, and we will be presenting our prospective audience with something that is flashy and intricate and pretty and, ultimately, empty. Like Minkata. Like Jalak. Like MOUL.
As I said over there, I am quite prepared to be the world's biggest bore on this point, till it is either accepted or convincingly refuted, at which point I promise I'll shut up.

Lots of possibilities. Disagreement between explorers on the principles and practice of Age Writing, or how best to follow the beliefs of Yeesha (if at all). Discovery of new threats to our safety and how we choose to deal with them. Possible exploration of whatever D'ni Ages we might have brought with us (this depends on how draconian Cyan might want to be about enforcing copyright: whether they're happy if we just avoid their created story and characters (Atrus' family, the DRC and the Kings, basically), or utterly forbid even the use of the terms "D'ni(TM)," "Linking Book(R)" or "Age{C}." We just don't know yet.) Whatever is decided on, the main story will need to involve the audience, to tell us something about ourselves. Doesn't have to be startlingly new--Cyan got four games out of variations on children rebelling against their parents. As for the fifth, I think that possibly suffered from the same problem as MOUL: "we've made this cool Tablet thing: what kind of story can we put round it?" That's a story built round the puzzles, and it really didn't work.
As I said, there are lots of possibilities. We just need to make sure we pick one before we start to design, whether it's an individual Age or our entire game. Because story is core.