Transportable != mobile. Compliance could be achieved by, for example, powering it from an external 120v circuit via extension cord, or a double-pole double-throw switch that disconnects the battery from the vehicle and prevents vehicle operation while the repeater is in operation. Tapping the signal line to the "BRAKE (!)" light on the dash to enable the repeater controller is yet a third option. This is an engineering problem, and it is fairly tractable. I may not have the patience to hack together the fanciest options, but running the gear off an extension cord should be quite simple, and would in fact allow me to locate the whole kit 'n caboodle in a truck tool box that can be moved, removed, or carried up a freight elevator if a rooftop is available and convenient.
Exactly the edge-case I have in mind. Besides that, the balloon-lofted antenna in my hobby project simply cannot be deployed in motion, or you won't have a balloon-lofted antenna - or any antenna - very long. I was planning on something to support a local festival like the Highland games, and people enjoying themselves there. (PS, really don't use that thing around power lines, and especially high-tension lines. )
I'm working on it. But mostly this stuff is already available to amateurs, and does me absolutely zero good 'cause nobody else I know has, or is willing to, get an amateur license. If they give me a justification, it's either due to not being arsed to study, too much hassle, or perceived toxicity in the culture surrounding amateur radio. "Pushing forward the state of the art" as used here is really about improving the products available to customers via retail channels. Finding new handies that are repeater-capable is an exercise in scouring eBay for new old stock. I think the only products available are the TERA TR-505 and the BTECH GMRS-V1; the former requires PC programming and won't cover all the channels in the service, the latter requires … actually the BaoFeng meets spec IMHO.
I mean, if nobody makes it yet, there's always Kickstarter…
Not that I'll be ready for that until I have a few more years' experience under my belt, but I still really like the idea of a combination satnav and 50 watt GMRS radio.
I don't think you have to go to fancy extremes to be compliant. Just don't operate with a balloon tailing behind you on the 417!.
"perceived toxicity in the culture surrounding amateur radio"
I am a ham and have seen this time and again. Folks ask on the board how they can get reliable two way communications for family and the answer right away is to get a ham license for every member of the family. I know of a few families where that is the case, but they are unicorns. Then there are the FCC "Nazi's" who look for an infraction in every sort of activity not positively supported by the rules, or twist wording to favor their prohibition de jour. Fact is If it is not specifically prohibited it is probably OK, The FCC's GMRS infraction filing cabinet buried deep in warehouse 13 in Gettysburg is mostly an empty drawer. The few NAL's they write are commercial users on GMRS channels. Or GMRS operators that are jamming part 90, well one guy from California basically. The filing cabinet for Ham radio infractions takes up three floors.