We know that AE7 and AE14 are full (a few slots open up every day as inactive airlines are removed). The other worlds only have a few years left in-game and plenty of open slots, so new players should feel free to use those as practice to become familiar with the game before the next round starts.
As this revision involves major renovations, both for the user interface and under the hood, it has taken us longer than originally anticipated. However, the changes are well worth it in the long run, minimizing bugs and speeding up future development.
For screenshots and updates on our development progress, see the new Developers' Blog (updated every couple of days now).
Thank you for your patience.