According to this CR blog article:
Electronic stability controlómore models going standard
So the mandate goes into effect for 2012. And now Tesla has extended Roadster sales into 2012. So therefore it's being forced to add ESC, I suppose. I wonder if it was working on it anyway. When I spoke personally to Elon at the Model S unveiling in DC Jan 2009, his response to me about ESC was to the effect of, "No, why would the Roadster need ESC? It's not going to flip over."While many models now offer this life-saving feature as standard, there are still a number of vehicles where it is just optional and several that donít offer it at all. Some of these models will be phased out or replaced before the NHTSA mandate takes effect [in 2012]. Tesla has said that it is working on ESC for its roadster.
If they do add ESC, I hope it's a retroactive upgrade possibility. Probably a tall hope, though.