So each group of players would be collaborating in a way to create a larger story that encompasses the entire world? Like what happens in one fort might impact the story told by another one?
It sounds like it could create a pretty enjoyable story, especially with all the oneupsmanship that would inevitably occur.
The learning forts sound like it could be a good idea, but since most succession forts move more towards creating Fun than creating an impregnable and stable fortress newer players might not learn as much. It would also only give them vague outlines of what to do and in what order due to the fact that most of the succession forts mostly give the generally summery of what they did, not how it was done.
Overall I like the idea of the multiple forts in the same world, a person dies in one fort and then they show up at another, or one fort "hears" of how one fort fell and swears vengeance on those that destroyed their sister-fort. There would also end up being little contests to see if a person could create a more impressive mega-construction, deathtrap, tantrum spiral, than the other fort, or possibly try and outdo what they did in the first fort. The only real problem I would see is that having multiple forts going on in the same thread would get confusing rather fast. There would have to be a mother thread where the first fort begins and subsequent threads created for the other forts getting more and more unwieldy with the addition of each fort...
In the end though the best thing to do would be simply to try and start one up. Start with a small two team world, the initial thread setting up the first teams and then maybe two new threads created, one for each fort, then watch the story unfold from there.
If something like this does get started than I'll definitely try and join in though, the potential here is impressive.