G-CPTN,
I remember reading (some time ago) about a device that was going to address the huge fuel wastage caused by taxiing. If I recall correctly it was some kind of electrical motor which had an unbelievable amount of power, making it capable of pulling aircraft up to the size of 767s. I'm sure the designers were having difficulty creating a form that guaranteed the performance that airlines would demand, which would explain why it hasn't entered the market yet. Hopefully others can provide a link.
Regards
VC10 Rib22
