I can't speak from experience as an author (I don't really have any, here or there), but Shifti is a repository for fiction involving shapeshifting, and it's a MediaWiki. The only complaint I've seen there is that uploading a single extremely long story has caused problems, which is easy enough to work around. On the other hand, the authors at Shifti aren't (generally) working on a forum and then transferring, so maybe that's causing problems.
Speaking of AO3, I've poked around there and it seems like a great place. As long as there are links between FenWiki and our presence at AO3, I can't think of any potential problems. (I'm pretty sure the Wrangulator is an actual functioning part of Fenspace-AO3's datanet. A handwavium quirk: Tag Wranglers, by participating in the steampunk sim environment, make the system do a bit of wrangling autonomously. If a Wrangler who is capable of joining in refuses to do so, the server expresses its displeasure by acting (to that person only!) as if it were under heavy load: dropping connections, noticeably lagging, and so on.)
Speaking of AO3, I've poked around there and it seems like a great place. As long as there are links between FenWiki and our presence at AO3, I can't think of any potential problems. (I'm pretty sure the Wrangulator is an actual functioning part of Fenspace-AO3's datanet. A handwavium quirk: Tag Wranglers, by participating in the steampunk sim environment, make the system do a bit of wrangling autonomously. If a Wrangler who is capable of joining in refuses to do so, the server expresses its displeasure by acting (to that person only!) as if it were under heavy load: dropping connections, noticeably lagging, and so on.)