There's a decent amount that play off and on. Nothing consistent. And GD is more focused on SP.I haven't even looked into the mods yet. After all these months of playtime, I've only got 2 chars so far, and only 1 at lvl 100.
And I've only scratched the surface of the Crucible mode. I mean, this game is so deep, I really wish we had more of a following from people here.