Intermeccanicas are available with heated seats and gas heaters, so both are possible. Both can also be added to any car.
Adding heated seats requires removing the seats, removing the skins from the seats, and adding the heaters. Most towns will have at least one upholstery shop that can do this. Should cost about $500.00. You also need the alternator capacity to run the heaters without killing your battery. The test is, everything in the car should operate, and the car should still run, without the battery connected. (Start the car, then disconnect the battery).
Adding a gas heater requires clearing room under your dash for the heater and making a mounting bracket. Beyond that, the installation is very simple. The kit I get includes all wiring harnesses, all gas lines, "T"s and fittings, inlet and exhaust, etc.
The heated seats heat your back and butt, which I have found don't get cold anyways. The gas heater produces so much heat that you can defrost the windows of the car behind you if you have the top down while driving, or you could just turn the temp down.
Ron from rainy Vancouver.