Reviewable (https://reviewable.io) has strong support for a rebase-centric workflow while still integrating pretty well with GitHub. Once somebody has reviewed a commit it never disappears, even if you rebase and force push (special refs keep them pinned in the repo). You can easily get incremental diffs between the old and rebased branch or individual commits.
I'll shortly be deploying a new feature where Reviewable will try to match up rebased commits with their predecessors and automatically pair them up when diffing. This is just a heuristic based on commit messages but it works pretty well for non-interactive rebasing. Otherwise, you can still manually diff any two revisions you'd like.
I'll shortly be deploying a new feature where Reviewable will try to match up rebased commits with their predecessors and automatically pair them up when diffing. This is just a heuristic based on commit messages but it works pretty well for non-interactive rebasing. Otherwise, you can still manually diff any two revisions you'd like.
Disclosure: I built the tool.