Last-update user look-ups creates problems for large controlled vocabularies

The new Instance reference tables are by far the longest settings tables we've seen so far and they surface a performance issue.

The Settings components make one users/ look-up per term to find the name of the last-update user and there are several hundred contributor types for example. Lots and lots of pending /users requests can thus back up in the client and create problems for the UI and possibly the back-end too.

Looks like some sort of caching or bundled look-ups or a server-side join might be needed.