FTR I've just documented the Unstable annotation here:
*
http://dev.xwiki.org/xwiki/bin/view/Community/DevelopmentPractices#H40Unsta…
*
http://platform.xwiki.org/xwiki/bin/view/DevGuide/API
Note that I'm not especially fond/proud of the max time strategy we have since it can
lead to APIs staying for 2 years but at least it makes it easy to implement by checking
for @unstable before each "N Milestone 1" release.
Another option would be to automate the check in a Maven plugin (by reading annotation and
then reading @since javadoc tag) and keep @unstable code only for , say, 6 major releases
(which corresponds to 1 cycle length).
Thanks
-Vincent