Was a mention system ever discussed e.g. @UserName (rep-like notification as a result)? I tried searching around but couldn't find a thread. Discord has adopted it recently as part of their functionality but I believe it was originally an idea older than them (twitter?).
I believe it's this mod specifically after a tiny amount of research but I've never tried installing it.
https://www.vbulletin.org/forum/showthread.php?t=242733
I admit I find it especially useful on the org, whenever people want to get my attention.