Thanks for posting @wolftorn! I think that I’m finally convinced that they are valid use-cases for this.
I’ve created an experimental branch in https://github.com/plotly/dash/pull/140 and https://github.com/plotly/dash-renderer/pull/25 that adds support for this by adding a PrevInput parameter in the callbacks.
I’ll keep those PRs updated with progress. It may take a while for this to get released as it is a substantial addition to Dash’s (minimal) API.