Feature request: convert bundle plus overlays into flattened bundle

I'd like to request a Juju feature, or perhaps an idea for a Juju plugin: a command which would take as input a bundle and one or more overlays, and generate a flattened bundle, using the rules that Juju itself would perform for combining bundles/overlays at "juju deploy" time.

This would make it easier to compare deltas between bundles stored in git (e.g. Field's repository of bundles deployed for our customers), or to compare such a bundle to the output of "juju export-bundle".