If they inforce something like this, then traffic lights should have some sort of visible timer, so in the event someone rolls up to a red light and as soon as they switch off the engine, it turns to green, it would prevent traffic building up behind the person who then has to restart their car.
I think most people would just crawl upto red lights slowly as a get around making it very hard to enforce. Are they going to have traffic wardens at every set of traffic lights then?
TBH, i think its daft, as mentioned older cars dont like starting once hot and require more fuel to get started again.