This is a very good idea, Arminius. However, it is fraught with difficult obstacles. You don't want TOO much heat, or the grease is going to liquefy and drip out of the bearings. You would need sensors to monitor how warm the hubs and bearings are.
Sitting still, the hubs and wheels are going to be huge heat sinks, wicking the heat out of where you want it. Your idea of insulation would help. But how do you do that?
Once rolling down the road, not much heat is going to be needed, as friction will keep them up to temp as usual.
I'm thinking some kind of resistance wire element wrapped around the bearing area, PWM controlled with a temp sensor on each hub. If you don't overdo it, the gains of warmer bearings
may outweigh the induced alternator load.
Oh, and it should be able to plug into an outlet while in the garage, as well as be self-powered going down the road.
Your first version will most likely not be ideal, but I think it's very worthy ecomodding territory! Do it!
