There's also a certain amount of anticipating legislation related to NOx emissions and noise here as well. Since airport communities are pressuring governments over local air quality (I know - there's more gas coming out of the bus that takes you to the airport...) and engine noise, this seems to be a reasonable solution. More especially so if, in the longer term, you can do away with the APU and use a hydrogen fuel cell in its place. Back of a fag packet calcs show the fuel saving on a taxi out at CDG or AMS vs. the penalty of flying around the dead weight on a 500nm sector to be well worth it.
Given the potential pitfalls of electric taxi I'd rather Boeing be the first to deliver such a system
Only provided it doesn't spontaneously combust...
