I don’t know about other states, but in NSW a “pink slip” vehicle inspection is required every year (once a car is 5 years old) in order to renew registration. The odometer reading is recorded as part of that process, so the incremental administrative burden is zero to calculate an RUC from that already submitted reading and then add it to the registration fee which is paid online.
Well not quite zero, for the first 5 years of any new car’s life, the owner would need to self-report that number prior to renewing registration. If they lied at any point, it would catch up with them in year 5.