Feature suggestion: "Urgent" tag

I mentioned this in this tweet https://twitter.com/AdrianKClayton/status/1230289975561740288?s=20 and was encouraged to post it here. Essentially it would be the ability to choose someone and tag them as "urgent" or whatever term you want to use, so that whenever they send message you get notified as of you were directly mentioned. This could be like a "if they message in this server" or just "if they message in general". It occured to me after someone did me a favor and I was thinking "I wish I could get specially notified if this person says something so I can help out if they need". I don't know how viable this is, or how much help it would actually be, but I though I'd share the idea.