The problem with opening up an NA East Server is that it would force a dispersal of players from the centralized NA Server. Basically this would mean that if you have friends on the west coast and you live on the east coast, you can't play with them. For a country like the United States or Canada that spans from east coast to west coast, separating the country into east and west isn't a feasible solution or plan. What they are most likely working on is trying to centralize the servers into the Mid-West which would balance the ping between east and west, or they are trying to work on distributing server load more dynamically which should slightly lower ping on the east coast without increasing the ping on the west coast. Either way, this isn't an easy problem to solve, nor is it a cheap one.
By the way, as far as the actual ping value, 90 is perfectly playable, you really don't need 10-20 ping to play effectively. I regularly deal with around 83-108 and it is easily low enough to have good responsiveness and doesn't cause issues like rubber-banding or jumping.