Bezier curve paths; Convert functions; User Media recording; Loads of bug fixes.
3rd party addons will have to do the same thing that built in addons are already doing, it's the same API. Unfortunately each developer needs to implement this individually because there is no way of knowing how a behavior or plugin should handle updates to their inner properties at runtime.
None of the details on how to update an addon had been made public yet, because the feature is still under development.