If I was ever to get around to putting up a role-play of my main story project's setting on this site (I've hosted it over other places, from forums to messenger programs), there's no doubt it would fall into the whole multiversal opera scale of the spectrum, but it could also be broken up into individual arcs or events, making each part more self-contained, since all of these role-plays would be considered "non-canon side stories" that simply use the setting. This is one of the reasons I've always found my setting requires an entire role-play forum, rather than just be posted on a public site like this as a single entry; the world is simply too complex and deep, but that's only a bad thing on a site like this where a role-play is usually composed of a single thread. Even so, I believe my setting could cater to both worlds you're describing, simply due to the nature of how I can set up the stories. I've done precisely the type of short-term role-plays you're describing using my setting with some of my circle, and there was no lack of depth or absence of complexity, for either the plot or the characters.

Outside of my primary work, however, I have a particular role-play brewing right now which could be the sort of thing you're referring to, although admittedly it will focus (mostly) on ordinary humans, at least in terms of their abilities, but I would also hardly call this role-play a "slice of life" plot (it basically focuses on murder mystery). A very important thing to keep in mind, however, is that it would be an elimination-based role-play. So there would definitely be a contained and inevitable ending for this role-play, because players would actually be getting killed off as time went on and everyone who joined would need to be able to accept this fact. The group would need to consist of at least seven players, however, though it could cater to more so long as the number remains an odd one. Assuming it was an odd number, a smaller number would also be possible, but there's a chance this particular plot would lose its quality if that happened.