I have previously made this suggestion, but nobody appears to be interested. The Broadcast Maximization Committee put forward a very well thought out proposal to do this in a new all digital band, contiguous to the present FM band at 76-88 MHz. I think their proposal has merit, and could be patterned along the lines of the DTV transition whereby existing stations would continue to transmit analog in their present bands while receiving a new digital channel for use in the new digital band. After a prescribed period of time, the analog stations would shut down and either stay on their existing frequencies or move to the new band, using digital transmission only.
On the other hand, I am starting to wonder whether digital is the right way to go as far as reliability and robustness is concerned. Now that we're past the DTV transition, I find that I can't watch many of the channels I used to be able to receive, and those that I can receive do not come in reliably. This is with a very high end antenna and preamp system. TV is largely a stationary service, but radio includes a significant amount of mobile listening, which adds more complexity.