You technically could, but wouldn't the complexity and the cost of migrating over to a system like that completely outweigh the benefit you could reap? Think of all the cars that only have FM/AM tuners, and all the stations that would lose listeners the moment they transition their programming model over.

Not to say its a totally awesome idea in terms of features and functionality. The amount of inertia it takes to move away from a proven technology wouldn't let such a system see the light of day.