This is a very interesting and creative idea. However, I don't think it would work. During emergency braking, friction heats the tire tread quite hot anyway, so I doubt additional heat would really be helpful. The electrical current will have to flow through an electrical conductor, but the tire tread, being rubber, won't conduct electricity. So there would need to be some other conductive material for the current to pass through. The conductor would then get hot, but the heat would then have to flow from the conductor through the rubber to reach the tread surface. This would take too much time to do any good. Moreover, the rubber would start to melt first where it's in contact with the conductor, which would likely cause the tread to separate from the tire. If you mix some kind of conductive material into the rubber, you will still have the problem that the tread will be conductive, and will thus melt, inside the tread instead of just on the surface. If you only put conductive material on the surface of the tread, it will wear off after a few thousand miles of driving.

I've used lots of theroelectric heaters in my experience and I can tell you that it would take thousands of watts to make any difference in tire temperature. Also, hot tires may brake better than cool tires, but I doubt the average driver could even tell the difference.

Also getting that many watts to a spinning wheel would be very difficult, with contacts, etc.

I propose a modification to your idea--install the brake disc to the wheel-rim instead of to the hub--than your braking heat automatically goes to heat the rim then tire. I know that this has been done on motorcycles. Still, you have to replace the rim during a brake-job might be a bad thing.

I do wonder if it would make any measurable braking improvement.