I've not officially heard of anything like this, but I know this will exist for TV sets simply because of the huge ration of analog sets still in use.
I already know of radio guys building other types of AM modulators for things like Xm radio, Sirius, etc, and since this circuit is relatively simple to build I'm certain that converters will be available.
There will most definitely be converters for FM available, so imagine having two converters to make your AM radio work! Digital to FM, FM to AM!
