I still like TUF. It's a completely different beast in my opinion. I would say contender series is a good gateway for future TUF participants in the sense that if you won on contender series but didnt get a contract your probably perfect for TUF. And even some looser's might have been exiting enough to be given a shot just for turning up and doing their best.
After all winning TUF is a lot harder then winning one fight on contender series. It's a psychological test as well. And TUF can build you up as a fighter being able to train with the best and all that.
I think they can well co-exist even in the future