The studio can be for any creative work, not necessarily just SotE related. :3 (As an aside, for anyone else reading this, I would say probably to keep fanart and fanfic to a minimum, if only because this is an original board and it would seem out of place to post a whole bunch of that.)
We do keep the OOC areas to PG-13 like levels, so yeah the Studio wouldn't be the place for erotica or explicit violence/really dark stuff. Livejournal and Dreamwidth each have huge communities of creative writers and no content restrictions, plus lots of opportunities to connect with other writers. I highly recommend them both, personally. There's also
adultfanfiction.net, which despite the name allows for original work too. :3
Oh! There's also Archive of our Own! Great place for posting fiction. It was originally made for fanfiction as well, but there's a place for original work, too. A well-made site with good features and strong community. No content restrictions, either.