Technologically, we're already there. ABC offers their entire lineup in HD online, and other networks such as NBC, CBS, FOX, and Discovery are starting to follow suit.We aren't there yet, and believe that it will be 5-10 years before this is possible worldwide.
At this point, all that's needed is the cooperation of the networks.
If Apple left the TV download business, and offered streaming through iTunes (and Apple TV) with the cooperation of networks and advertisers, they'd generate a market with far more promise and future. Right now, all they have to look forward to is a dead end.