My understanding is that there was a push to modify the U shaped tow trucks they use to position planes to have a battery powered system to start the engines.
The idea being that the APU isn't particularly clean burning, not compared to power plant emissions. It's been a long while since I've heard anything about that plan, for or against.
Interesting! Although it'd (presumably) only be useful for the 787, short of heavy modification to existing aircraft. Even the Airbus A350, an aircraft from the same era, uses a traditional bleed system. If planes continue down the bleedless route I can see it happening.
The idea being that the APU isn't particularly clean burning, not compared to power plant emissions. It's been a long while since I've heard anything about that plan, for or against.