There ain't gonna be no coating on a stainless steel antenna. There's a reason it's called "stainless." It's notoriously hard to coat with anything and get it to stick for any length of time. Try coating your silverware with something and see if you can get it to stick. Can you imagine the outcry if Apple does coat it with something and after 2 weeks it all starts peeling off?
As long as Apple keeps the antenna on the outside and they keep making them out of stainless steel, there's never gonna be a coating. So if you're waiting for Apple to announce some new iPhone 4a or iPhone 4v2, don't hold your breath.
FYI - The stainless steal band is not the antenna.