New worlds are coming to BOTH datacenters. Read the posts on the dev tracker if you want confirmation.
They are also doing other changes.
Some worlds are likely to continue being full until world transfer service is available.

It's designed for up to around 5000 concurrent players per world (obviously with a higher cap for total number of characters created), and unless they add more zones to spread out the players on, that limit is not likely to change. It's far from fun to try to play in zones that have too much people in them.