§95.631 Emission types.
(e) No GMRS or CB transmitter shall employ a digital modulation or emission.
The rules do not currently allow it. I doubt we'd see a big change anytime soon. FCC moves at a glacial pace when it doesn't involve bringing in money. Since GMRS brings in little in the way of licenses fees, and services like FRS, MURS and CB bring in zero, it's likely that nothing will happen for a very long time.
It would be nice if the FCC started to allow some changes to the personal radio services. Not sure what it would take, maybe radio manufacturers pushing for a change. The general public seems to have little impact.
There have been waivers granted, most noticeably the Garmin Rino's being allowed to send GPS position data.
It would be really nice if they'd at least allow CB to use FM. Many nations allow FM on the 27MHz frequencies. Since that would allow CTCSS squelch and some better audio quality, it _might_ create some new interest. Being able to block out unwanted noise would be welcome on the CB wastelands.
GMRS/FRS could benefit from digital, but I don't see it would add much to the service. The usage is pretty minimal in most areas. Some metropolitan areas do have all the GMRS repeater paris used up, so there might be some minor benefit of creating some new channels by refarming the band.
But, like I said, there isn't much call or much pressure to change things. There was some rumblings about some new GMRS rules in the works, but that's all been stalled for close to 10 years now.