Given my collection has been flagged X times by X unique users (where X is a configurable global $wgGatherAutohideFlagLimit)
my collection automatically gets hidden

When a collection is flagged it cannot be viewed by anyone other than the owner of the collection.
When I (the owner) view the collection I see a hidden tag.
I receive an Echo notification when my collection reaches autoflag status. (to minimize coding effort, it is identical to the echo notification one sees for a hidden collection)

Administrators can visit the 'auto-hidden' collection list, similar to the hidden list and either 'keep hidden' or 'unhide' (if backend allows).