Yes, when I tried to play yesterday, every NA server was full.
Right now the number of people playing and the number of hours people are playing are both very high. Later, a lot of people will quit and a lot of people who still play will play for fewer hours, so the servers won't be as stressed, and I imagine registration will open on the currently-full servers again. It would be bad if SE added a bunch of new worlds that later ended up being ghost towns due to not enough players in them.