A recent spammer hit mediawiki.org with a bunch of spam topics. Another (non-admin) user hid these topics. When I went in to delete them properly with Nuke, it did not find any of these hidden topics to delete.

Nuke should list hidden flow topics as well for the mass-deletion interface, as it is likely a common occurrence where a non-admin helpfully hides it to keep the spam off the page in the interim before they can be properly deleted, and having to delete such topics one-by-one is a chore, to say the least.