Random thoughts/suggestions:
I agree with the turns. The original poster in a succession game needs to be able to enforce the rules (without sounding like a jerk, lol), and ensure that things keep moving. A little more structure in the OP doesn't hurt, either, as well as keeping track of who's played, and little details like how many forts each player made, and what their fort names were. It'd be cool to see how many forts 50 players could make... Though, realistically, probably only half of those would finish their turns.
Another thing that would help is encouraging players to take screenshots, rather than draw maps. While I admit that the latter would be more fun for roleplaying purposes, it's a bit more effort than a lot of people are willing to put into the game. If we manage to build even forty fortresses, it would be difficult to keep them all straight in your head, and having seen screenshots probably wouldn't matter anyway, unless you went and intentionally checked the thread for them while you were playing.
The reason I suggest this is that it would help keep the thread active. Another possibility is to point out that, unlike traditional succession games, it's completely fine to post stuff about your forts (stories, pics, etc.) after your turn is over. But these are just ideas.
50 turns would only happen, I think, if people were given exactly one week to repost the save. They could build as much as they wanted (and as many fortresses as they wanted) during that time, but they would have to give up the save exactly one week later or they'd be skipped. As far as I can tell, that didn't exactly happen with this thread... I think that was the original idea, though.
Also, I agree with Japa... I'd like to be able to see clearly in the OP what was modded in/out, and what the rules are, rather than go dig through a number of pages.