The client isn't going to be that mind bending at first, it will just hopefully be a bug free version of the current client that we can then modify over time to add new features.
If the client isn't going to be that mind-bending at first, as you say, I suggest and strongly recommend releasing it with a new level cap (level 75) to make up for it. Surely, it will be the best timing for it, and the players will be happy. Mark my words.