SDK will never be active again, at least in its current incarnation. There aren't more than like 50 people that I've seen who still use the site somewhat frequently.
As sad as that is, it's the truth. TBH I think Hull should start (somewhat) over and capitalize on the release of the NX when it comes out, then we could kickstart this community again. It wouldn't be the same, but it'd be the closest we could ever get to the old SDK days. I don't frequent this site, though, so I'm not sure if Hull actually still works on it. If he did decide to build a new site for the NX at some point, that would be cool, but I doubt that'll even happen.