Proper warm up still required
Thermal cycles are stressful things for engines, especially going from idle to takeoff thrust. Presumably this means that the engines will still need to be started some minimum time before reaching the runway. If HERON becomes a common thing it'll be interesting to see if there are more rejected takeoffs or engine failures and emergency landings.
Tugs are slow, the need to dispose of the tug in a place where it can easily return to the apron without causing congestion on taxiways or the runway will perhaps limit this at some airports.