We have a prototype.
Phabricator provides staging now. Each stage is just a tag. Jenkins could treat each tag as a separated pipeline. This way we have one configuration for every build.
Ideally Jenkins Multibranch project would provide a tree view / folder structure that splits branch and tags at slashes. So ‘phabricator/D474’ would create a folder ‘phabricator’ with pipeline D474. Once a diff is landed the pipeline disappears. This resembles Jenkins workflow for GitHub pull requests.