I think the source for this was lolipuni, so I'm sure it's real. The mangaka himself has drawn ero doujinshi of the Tsukiyomi characters so it's not exactly surprising.
Although technically it wouldn't scale, I think restricting synonym editing to moderators would be feasible, since there only seem to be a few we need to keep track of.
Tag suggestions unfortunately had to be removed because it just killed the server. I think the complexity was exponential, per tag. Buffered got it to a low constant but it was still slow.
I've been thinking of caching suggestions as an extra text field for tags. Users, if they wanted, could refresh these against the current database, and the new suggestions would be cached. So they'd be a little out of sync, but it'd still be a lot better than a dozen requests per second asking for suggestions.
I've been thinking about how to add support for tag synonyms lately. A slightly technical discussion can be read here: http://trac.donmai.us/trac/ticket/78
The gist of it is automatically rename a synonym to a preferred tag. This wouldn't change how you search or tag a post, everything would be automated behind the scenes. A question would be, who should be able to add new synonyms, and are there unseen issues, or perhaps better ideas?
