Ideally yes, but the first time a kid gets killed because the school bus's transmitter fails there will be hell to pay. Will that be the fault of the passengers

Ideally yes, but the first time a kid gets killed because the school bus's transmitter fails there will be hell to pay. Will that be the fault of the passengers in the car? Or the car's manufacturer? The school bus's manufacturer? This infrastructure will need distributed two-phase commit. For safety-critical issues like school buses, eventual consensus won't be good enough. And then you'll need an infrastructure that detects when an older or simply defective car is present but not participating in the protocol. These problems are all solvable, but they're by no means trivial.