NBA outlines plan for professional sports leagues pushing for national legalized wagering
Too much money to be made for this not to happen on a soonish time frame, I think. Once the Supreme Court says that states can legalize sports betting (and the Court watchers say that is how they are likely to rule), many of them will. And the leagues are going to be part of it so that they can get their cut.
I say within 5 years, betting on pro sports will be legal and readily available in the majority of states.