Hello Brian,
I'm glad to hear you're switching to django CMS.
The undo/redo functionality will come in our next 3.4.x release as its being developed separate from the core. And the permission enhancements landed with 3.4.0
In regards to the REST API and 3.5.0, we still don't have a deadline but the REST API is planned to be compatible with django CMS 3.4.x :)