Of course it would. But there is no downside. Conversion kits exist to transform current models over to nat gas (most vehicles anyway). Regular gasoline would remain available. New cars would be required (via emissions standards) to be nat gas within that time frame. As long as we don't give up power (cause we all know we love the horses) or safety, the public won't care as long as they aren't inconvenienced by a lack of availability of pumps. Which is where a mandate comes in from the Fed that all gas stations begin transition/addition to be up and running within the time specified.
I am not going to pretend it will definitely be within 3-5, but I do believe that is a very workable time frame. Add in expansion of oil production and R&D into clean/alt tech and we can hammer oil prices into the ground. We import about (I think) 60% of our oil. Transportation uses about 70% of our oil consumption.
The case for the switch is there. Add in the benefit of keeping the jobs and the money here in the US and the public will be on board.
Just my thoughts on the matter... I don't anticipate either party actually pursuing such a plan.