Air quality
If they can get this working with electric motors (or at least hybrid) then another plus is the definite potential to improve safety and air quality on the ramp - although I love the smell of burning jet fuel - engines often burn oil and other crap when starting up, and if you're working on the ramp every day it's probably going to take a toll on your health.
If each aircraft just has to start a relatively small APU with an exhaust that's high up, rather than starting two or more jet engines down at person-height, I'd expect that would make a difference. Don't start the engines until you're on the taxiway out in the open and the startup smoke dissipates where there's nobody to directly breathe it in.
Could also reduce the likelihood of foreign object damage, as well as reducing the likelihood of workers being ingested into running engines.
All low probability, but high cost/impact issues which probably add to the overall business case.