This is somewhat addressed by the inclusion of globalusage data for the _target wiki in the latest version, but I'll leave the task open in case someone wants to spend some time and effort trying to efficiently return only images used in articles on the _target wiki. In the current setup, I think this would at least require a new CirrusSearch index and query feature. It was discussed a bit in T220282.

I think there's adequate randomness in the new endpoint, so I'll edit the ticket to remove that, but I might not be understanding the point there, so feel free to modify as needed.