Read the papers, people. Whether it's misguided or not, aviation is in the cross-hairs at the moment and has to be seen to be at least thinking about doing something.
Anyone who's sat in the evening departure queue at Kennedy in the last year or two cannot but have thought about how much juice is being spewed into the atmosphere. Some posters on this thread have called for independent evidence - well, that's what a trial is for. It may well be that, taking into account the cost of buying and running all the extra tugs needed, the impact on arriving a/c of having to perhaps taxy around departing a/c under tow, etc. might stop it in its tracks. Then again, it might be that a tonne or two can be saved per 747, per departure on average and over the life of the a/c, that's a saving that any rational carrier couldn't sneeze at. Management is also under a duty to shareholders to constantly look at ways of cutting costs.
Starting grids? Little different from de-icing grids at some airports or the little circular holding bays that some airports used to have near the runway ends. Kennedy already has engine starting points off the taxiways - so not a totally alien concept - so it's just a matter of moving these out on the field (ok, a bit of construction will be involved).
Engine probs due to cold starts? OK, so f'rinstance at Kennedy, rather than have all 4, or both, running for an hour or more in the queue, start them up (or the ones which weren't started straight after push-back) out on the field with 20 or 30 mins to go (I don't think anyone's suggesting going straight from the start point onto the departure runway).
Aviation needs to be seen to be doing something. It is in the interests of all those in the industry to look for ways to cut emissions (and costs). Being seen to be pro-active is better than being seen as having to be dragged along. This issue will not go away.