Alicornutopia

Each of the glowfic continuities so far has a fixed set of authors. Would there be interest in a thing that anyone can join?

I'm sort of conceptually interested but also deeply afraid of how slow it would be if you had that many people to wait on xD (I say this as 100% one of the aforementioned slow people.)

But really, most anything where other people come up with the plot instead of me I am on board for xP

I've participated in some of those before. The Milliways premise is from one, in fact. I find them hard to keep up with these days.

panfandomsandbox and mixed_muses on dreamwidth are both anyone-can-join sandbox hubs with a decently sized community of existing players (the two have very high overlap with one another), if anybody would be interested in those.

Marri: I'd been imagining that any given thread would only have a few people at a time, and if someone's not available then their characters stay "offscreen".

Kappa: ooo shiny

I don't think I've got the time to commit to another long-term RP thing at the moment, but I'd totally delurk for that sort of open sandbox idea with other glowfic-type people.

Are those good to learn how to RP?

Sure, why not?

You could, after all, learn to RP in any RP-type thing; the difference in an open RP is there's not as much pressure, since it's implied that people will be dropping in and out as time and schedules permit.

Well, speaking for myself, they're intimidating, Mostly from the sheer quantity posted there already.

There is absolutely no expectation at MM or PFSB that you have read any other threads there before starting your own, as long as you have a broad background familiarity with what the place is for and how it works. Other characters you encounter may have previous sandboxed continuity that affects them, but you don't have to worry about it. You can just make a post with a character encountering Milliways for the first time, and see who tags. "Character encounters Milliways for the first time" is a very common way to introduce a new character, a new player, or both at once.