The engineering challenge is that the E-cat apparently produces only heat. You'll have to figure out the best way to turn that into useful power. However the latest iteration of the e-cats are very small, you wouldn't have much problem fitting them in a vehicle.
Four of them on a desktop here -- each able to output 4.4 kW
If we can be in a scenario where E-cats handle home heating and electrical generation, then we'll have a hell of a lot of natural gas that can be used for vehicles. If E-cat can be used for powering ships and steam locomotives, then that frees up a hell of a lot of diesel for automotive use as well.
As always, this all presumes that E-cat is not a sophisticated con. If it's for-real, expect the Russians and Saudis to send agents to kill Rossi and destroy all his notes, because the E-cat would kill the economy of any nation that primarily relies on fossil fuel exports.