I had previously posted suggesting to rename Lock to Archive. I apologise, this feature is not needed at all. It should only be needed where a discussion is quite permanently closed per policy (such as a past request for permissions). In this case, such thread should be simply protected using the standard page protection tools available to sysops.
I worked out some more suggestions here: - https://www.mediawiki.org/wiki/Thoughts_on_moderation_in_Flow
-- svetlana