Wow, someone who didn't take a public statement personal. I applaud you. Seriously.
Rarity will be imbalanced simply because of the fact that people
expect a certain item to be rare. Because of that, most items that were rare, won't be.
A good example of this is (if you played RuneScape) when Jagex tried to implement Party Hats (rares) into the 07 servers. Everyone knew they were rare in the "normal" game, so everyone had the mentality that they would be rare also in 07. Thus, everyone horded them, too many were in circulation, and the price difference between the normal game and 07 was like.. 500k/1billion+.
What I think will most likely happen is different items will become rare. However, it is also based on how Amy decides to integrate certain items. How she integrates items will depend on if an item becomes rare.
(I know a lot of what I said had nothing to do with your post, I just said it for good measure. lol)