@Firstaide @maloki pardon me for butting in, but just a thought, I know it'd be a lot of work...
But I remember livejournal (and maybe google plus) letting you set up groups, putting people into various groups (non exclusively) and when you post, choose which group(s) see it. So like if you found a Harry Potter polyhedral dice set, could talk about it to your HP & D&D groups without bothering knitting group.
@maloki @Firstaide (y'know, if we're talking kitchen sinks here, and I would not envy a UI/UX person tasked with making that easy and intuitive...)
@maloki @Firstaide Totally understood. Just saw a wishing well and tossed in a penny on the off chance I could actually get a pony. :D