From what I understand, in the US the FCC licensing for fixed location transmitters, relocatable transmitters, and transmitting while in motion are different (sorry can't remember the official terms). These stations may not be approved to transmit while in motion, and so Starlink may put technical restrictions in place to prevent use while moving. The license applications they put in for ruggedised terminals, intended for marine use and the like, requested ability to transmit in motion, but I think these are standard terminals (certainly not gimbled or gyro stabilzed) and aren't covered by that license. We'll have to wait and see until people start receiving stations and testing them out.