Tracking branch changes across force pushes

Imagine a feature/x branch forked from the develop branch.
After some commits, a pull request is submitted, and the reviewers comment on some issues.
The submitter does an interactive rebase and fixed the offending/problematic commits - and then does a force push.

The reviewer would like to know what changed, but that is currently not available.
With tracking branches the branch before the force push would be preserved as "feature/x@20161006215817" and the bitbucket UI for the pull request could have a button "Compare to previous force push" that shows the difference between the old "feature/x@20161006215817" from before the force push, and the new "feature/x" after the force push. That difference would show the changes clearly.