Ability to request an human ack on a message

[ara4n]

Flag on a message to say 'i need to get an answer of some kind to this message'

[lukebarnard1]

I've had a vague idea related to this in the past where a mention = request for ack, and a reciprocal mention is the ack itself. The mentions could be scraped by some notification-management UI, where the user has a list of un-acked mentions that they can get to and check off one-by-one.