It would be very hard to build Leben as a challenger to Anderson's belt... Although I've ragged on Leben in the past, I'm starting to like him more and more now(maybe because he is kinda maturing), but Anderson didn't just beat Leben, it was one of the most dominating performances I've ever seen in MMA. Leben didn't get one amount of offense on Silva.
If GSP continues at his pace, I think they will get him to move up to fight Silva... Possibly even BJ Penn? They hinted at it yesterday.
If Leben can do as well as he has been doing against better competition they can very easily push Leben/Silva II to the public, you would need a second big match though.
I do think the idea of super fights could be the next best possible thing though for the UFC, as long as they're not retarded PRIDE like matches.