See, from what you say it seems you have the theory that actorslash that's not widely popular gets just lumped together with the fictional stuff for convenience sake because interests are likely to overlap for those who like it, and for those who don't it's not much bother because the numbers are so small, and once it gets popular there'll be separate communities. And I don't think it necessarily works that way, because I suspect that LOTRips is special in that people interested in the RPS often aren't much into LOTR slash so the interest/disinterest overlap of RPS and non-RPS fans was symmetrical.

In most other cases I've seen it seems more that almost everybody into RPS for a show will also read for the fictional side, but vice versa it's not true. So you get RPS fans for whom it's convenient to treat it as one fandom (with one newsletter, mixed RPS/FPS communities etc and just a RPS warning label like you'd warn for any other thing), even if the RPS fanbase was large enough to sustain fully RPS-based communities, and non-RPS fans who'd prefer RPS-free spaces, but will in the end sort through the mixed communities to read the show-based stuff of the RPS fans.