I think what you mean is "there is no new UI for beta testers, yet". There is clearly a new UI -- they show pictures of it somewhat often At least that confirms my suspicion.
My thought was the UI would be included in an update and there would be no need to activate it. When the UI is released, it will fully replace the old one. I don't think you will have the option to use one or the other. AND....I am quite sure we will see at least one thread where the users want the old UI back.