I had looked into inductive heating fer my truck a few years ago. I had to rule the oil pan out as it would eventually cause the pan to buckle over a number of cycles. I use an induction cook top daily in my household and I've expeienced what happens to a thin walled mixing that's heat cycled a few times.
I was looking into making one with its own heat exchanger to plumb into the cooling system so you would have to worry about damaging any critical compenents like the oil pan. It could heat up the coolant fairly quickly (15 minutes or less) compared to a standard block heater setup which can take a few hours depending on conditions. The key would be able to make the coil survive the road vibrations if it was attached to the vehicle.