Is it relatively active? The closest thing to roleplay I've done is probably DnD, so that's all I have to go off of.
Is it possible to find people who can just sit down and collaborate on their writing for hours, as opposed to sitting around for posts?
Roleplaying is inherently a pretty active activity, but it makes up in burst activity with the fact that people have easily dwindling interests. Expect to be dumped once, twice, one hundred times, often without warning, or if you're lucky with a polite 'I have no time/interest anymore, sorry'. I've lost count of the failed gigs. I don't even care about the count. It's the few successful gigs that do come together that keep me interested; kinda like how a true relationship works.
Burst posting, speed posting, etc sounds along the alley of what you're looking for, which certainly happens, though good luck finding someone who does that and produces something with fair quality. Chat roleplaying is probably the better method for you, which again has that stipulation that chat roleplaying is often of lesser quality/effort per post (though not always, depends on who you get). In any case, it's relatively unusual for how the site works, and so it is something you'd want to make an interest check for. From there you'll need patience. Even when you get someone, you'll still need patience.
And if you're dropped by someone, well, I find the best mechanism for that is to simply take whatever was created in what little was put together and stick it into my own lore. No loss when it's all blended into your content in the end.
