Being a designer, i think this 'could' be developed into something good
Depends on the budget, however so could any of the names already taken, tripletube.com quadtube.com and so on
It's not that brandble because it really doesnt stand out as anything, YouTube does, because of the 'you', DoubleTube...Double?? just doesnt ring any bells unless you set up a site that points out why 'double'... a two way broadcasting site or whatever maybe, i don't know, but unless it's dev. and marketed, it's not worht that much IMHO
Good luck though