Hierarchical modulation is possible on the digital transmissions and is in the specification, but I think the same people if not more would be complaining about low audio quality. On the other hand many people complaining about too many dropouts are not in the service area of the transmission they are receiving. Also many transmissions do not use the best configurations for the channels they are using, especially with changing conditions. Actually the settings determine the service area to a great extend.
A more interesting approach was done a few years ago using a receiver (or better even more than one) in the target area and use the feedback to alter the settings at the Tx, so according to the actual conditions the best quality for a given service area can be used at any time.
Btw the information given in the AFs often seem quite optimistic concerning the coverage area