That would be hilarious, and quite in keeping with the status of celebrities in our society as the new aristocracy. Gaga-coin or Bieber-coin - millions of fans would actually buy that sort of thing. I think they'd need physical gold coins though, for extra bling, or perhaps Gaga would go for pink plastic. Oh, just looked, and it turns out someone already thought of this but with dollar bills:

http://www.trendhunter.com/trends/pop-culture-cash-by-james-...