Actual answer is whenever Derek Wilson decides it's ready. Last I heard, mods (some? all? no idea) have access in order to beta test, and progress is being made on fixing all the weird crap with the vB transition. The open vB forum iteration we saw had a lot of relatively minor issues, so hopefully it won't take more than a month more (yeah, I'm being hopeful) to iron those all out. Derek really needs a staff for forum administration, but as I understand it's just him, and he's also has his main site duties and whatever else he does professionally/personally to deal with.