Beta test users of new Ecdesign versions will be able to run in both official and beta mode. Meaning you can decide if you want to plan the layout in beta or in official release.
Ecdesign 4.5 beta will support older layouts, but we do always advice you to finish a project before upgrading to a new beta version.
You can send in a support ticket if you have more questions about beta testing and how to be part of the beta software program for Ecdesign.