There is the possibility in a post to use the @ to look for a specific user (I'm not talking only about citing message blocks from previous answers). I believe it would be great to notice that user that he was cited and where. Notification could be an email or just a mark on the thread like 'new message'.
One could also think to add switch on/off button in their personal settings. I did not go into misago code so I do not know if its implemation is easy. Besides that, I'm wondering if it won't be very noisy at some point. open discussion.