Given that flags are intended to be used as a marker for "this thing needs doing," I feel like there has to be some way to display the total number of emails flagged for follow-up in a folder where you would normally see the total number of unread messages: 
If I go to the properties of the folder, I can see options to display either the number of unread emails, or the total number of emails. Is there someway to add to those options? I've searched just about everywhere I can think and I can't find any mention of someone trying to do this. Honestly kind of surprised this hasn't already been added by Microsoft; seems like it would be an incredibly useful feature for literally anyone who uses flags.