GitLab supports this. Every time someone pushes or force pushes it tags that as a version which you can diff. If your developers know how to generate new commits then you can do it right away with GitLab.

The problem is generating the new commits. Developers just aren't very good at doing this. They can modify a single commit just fine, but modify a commit that isn't the latest commit involves a rebase.

Magit has the "instant fixup" option which is basically like amending an arbitrary commit instead of just the latest. What is actually doing is doing a commit with `--fixup` then `rebase --autosquash`. This technique can be used manually. Fixup/squash commits should be part of all developers' toolkits.