Create a function in the bitbucket page for a repository to "release" a new version. It should have a field for the version number, name, and description. Then it should update the last commit with a tag matching the version number.

A separate event could be used called "release" or users could just hook in using the push webhook and check for presence of a tag to determine if a new release was created for a plugin, app, etc.

This feature exists on Github.com already.