Its not so much the community part that I'm worried about, but the marketing aspect... getting people to know the place exists in the first place. I think once people who are into off-topic chat actually find the site, they would be pretty inclined to stay.
Feature-wise I think it tops a lot of the forums out there today (note that my opinion maaay be biased lol). Most just use the generic phpBB or vBulletin, which is great if your looking for something very specific, but not so great if your trying to browse for interesting stuff to read. IMO, the system used here at Hacker News, Digg, Reddit, etc., is far better, but again, the limitation I see with that is these aren't so much discussion forums as they are news link networks.
But mainly, I'm hoping the main thing that will draw users is that they can post threads that are just links to other discussions that are interesting. So hopefully the site will become like a hub for off-topic/random/general discussion.
I wish you success, if only because it will draw offtopic posts across the internet to one place.