Thanks for sharing your idea.
Personally I believe that would break the golden rule that I have highlighted, because people would get it just by playing the game normally. So in the long run, people who got to rank 313 in GW1 would have put extra external effort in. Also some people would get lucky and get it fairly quickly, which seems to go against the idea that getting this character should require extra effort and dedication, and more specifically, extra effort and dedication that isn't simply just playing the game as you normally would.
I forgot to mention also that your idea would allow people to "buy" the character as people could buy in game coins until they get it. I think I recall a PopCap representative saying that they didn't want the Unicorn Chomper to ever be buyable and only earned in the game.