Why don't they just create a track and field "league" where they do not drug test - see if it's popular? All of the champions and records set would only count for that league - but how is that different than any sport that creates a league? If you look at how popular the UFC has become, and then other really fringe stuff, it is possible that people may want to watch people who'll do whatever it takes to win.
I'd watch. I am curious to know what people can achieve when freely allowed to do what they like. Would they be crushing world record times? Also, like body building, would be interesting to see the results. It also would give all the athletes caught doping other options to make money still.