I don't know that I would want to powder coat wheels, if you do any serious or extended amounts of driving anyway. The potential for heat build up and the resulting bond separation could lead to some pretty ugly looking results.
My point of reference was some misc brackets my Bro powder coated and put on his Jeep. Well, a couple of those were in close proximity to the exhaust system and over time, the powder separated from the base material and peeled up. Looked interesting to see powder peel and since they were just brackets, we replaced them. Don't know how that would hold up on a wheels where braking heat could be a factor. It is likely the wheels would have heat for the sustained duration that an exhaust produces, but heavy brakes use can produces temps that exceed the exhaust.