In general, nothing can be removed or modified in way that is not backwards compatible. If something is deprecated, it can be removed after a major release, provided there is a discussion on the dev list.
All public and internal APIs should have useful javadocs. For all public
APIs (anything not in /internal/), new additions to the javadocs
should include an @since tag to let the users know when the feature was
Any feature which is deprecated should specify a link to the new alternative.