"The short version is, the expansion adds a lot of new items and item levels. It expands the power of the game, all the classes are being rebalanced, and we’re adding new properties to items – even existing items, when new versions drop.The legendary thing and the new gem tiers pretty much takes care of a lot of that stuff."
I hadn't heard about any gem tiers being added above Marquise - have I missed something?
Gems are getting a overhaul, all gems!
We do not know the specifics just yet however, but those should be "better" in general since they just added the diamond gems and ignored the jewels which they were talking about and trying out.