For a few years there was a group that had an FCC issued experimental license for DMR on GMRS. It was limited to one repeater in one area for use by a small number of users. Request was essentially to test the use of DMR on personal radio services and to check compatibility with other analog users.
The applicant renewed it every year for quite a while, and eventually the FCC stopped allowing it.
It can cause problems with PL/DPL falsing on analog radios. It also makes the "monitor before transmit' thing pretty hard. Any consumer not smart enough to understand coded squelch is going to have issues with it. In urban areas, tying up a frequency pair for one special group of users isn't helpful.
No, if people want to play digital voice, amateur radio is the place to do it. That's where experimentation belongs.
If we really want to do digital on personal radio services, it needs to be very carefully designed and not a random choice by users.