I think natural gas electrical generation + electric cars is a lot more likely to happen than natural gas vehicles (CNG or LNG). To the extent that NG displaces coal (which is already happening due to cost of NG being so low, at least in the US; we could accelerate it with regulation or long-term fuel contracts when building new plants), it's a big win.

From a security (vs. environmental) perspective, burning US coal is superior to importing oil.