People really have no clue on where the greatest fuel savings in aviation come from. here they are fretting over tugging and aircraft to the runway to save some fuel, when airlines all over the world burn tonnes of the stuff stacked up in holds at congested airports.
Ever fly through Indian airspace? They need 10 MINUTES of spacing due to lack of radar coverage, so here you have thousands of aircraft transiting through their airspace at non optimum altitudes because there is someone 200 miles ahaead of them at the same level that they wanted. That costs airlines a darn bit more fuel than they burn taxiing. Want to go green? take all the money that you want to invest and go buy India a proper, modern radar environment. Presto you just saved millions of dollars in fuel costs a year with a associated reduction in CO2 emmisions.
Its a bit harder for a non aviation person to understand however and certainly much harder to fix than a nice simple solution like tugging an aircraft, so you never hear about it in the press.