wheel motors and "dead engine" taxying
The principle of regenerative braking is already very well established in the automotive and railway worlds...so your wheel-motors would ,presumably be fixed stators with rotating discs (hall-effect)...the disc could also be used as a brake-disc.
regarding the main engines, I understood they needed to run a while for temperatures to stabilise. Unlike a car, you couldn't just drive your overgrown electric golf-buggy to the end of the runway, switch from "drive" to "ignition ", light the fires and "balls to the wall"
so, you'd still need the engines startedwell in advance of takeoff.
would the fuel-burn be considerably less than running the APU?
what would be the feasibility of a big generator built-into the main engine(s) to power the gear-propulsion ? this could "drop-out" at a pre-determined engine RPM, saving mechanical drag.
(or is the on-board battery-system envisaged to store sufficient power for ground-manoeuvers?
Sorry if I'm talking crap! I'm not "in the trade"