That would be useful information. However, I need to be careful not to make the report too confusing for non-expert users. My idea is to add all advanced relationships to the Assets Browser report. By sorting by "Workshop id", you already get pretty close. Perhaps I could add sorting by "Workshop id, Used in city".

Honestly, ♥♥♥♥ non-expert users. they'll choke on their own shoelaces without hand-holding

perhaps add it as an undocumented configuration value?

I don't see why it needs to be unnecessarily complicated. Maybe just split "The following assets are currently unnecessary (not used in this city)" into "The following assets are not used in this city, but unsubscribing may cause issues" (with text under it explaining that) and "The following assets are currently unnecessary (not used in the city) and can be unsubscribed safely"