If fed can find some marketing guru to manage his line and wants to do some bussiness for his own line, Nike might continue to make fed lines like Jordan brand. I think there is a possibility.
Nike knows whatever they put "RF" logo, it sells ^_^. This matter might be another long discussion though.
Anyway, I don't think value will go up that much in my opinion.
As soon as fed announce his retirement, several items might go up but after a month, every items start to decline.
I understand several Agassi shirts are selling high nowadays but Since fed items were massive productions and many people bought more than one.
Also 10-20 years later, we might see another tennis star ^_^.
Men's Tennis Apparel