While buying some parts at the local GM dealer a few days ago I was talking to the counter guy who said that GM was going to this soon, he had heard in 2013 cars but maybe it would be phased in like R-134 was over a few months.

He quoted some figures that he said might not be accurate, but were close. R-12 will break down, when released, in something like 500 days. R-134 takes about 160 days. The new stuff breaks down in the atmosphere in 11 days.

I do recall when R-134 came out there was a big cry about using Propane but the DOT refused to allow it since it created a fire hazard in an accident. Of course the automotive press pointed out that gasoline never presents a fire hazard in a accident, but the DOT did not see the humor.