I'm a 313er and pretty proud of it. When it was announced after the beta I decided I was going to go for it. I was level 140 then and getting to 313 was one of the hardest things I've ever done in gaming. I do agree that the unicorn chomper should be exclusive to maxing out GW1 - HOWEVER. Gaming is all about fun, Popcap I believe are all about fun. It's actually not a bad idea introducing a system where current players of GW2 can earn it. NOT STRAIGHT AWAY mind you, out of respect for the players who went to the trouble. Maybe in 6-12 months or so (let us bask in our glory for a while). Then I'd make it really really hard to get, so those players can appreciate the effort too.
Something like promoting every existing chomper in the game to max level - not sure how many chomper are in the game now but surely thats got to be 300-350. Now that would be worth it.