I'm against concessions. When a game is lost i try to continue play, defend, score a TD.What's funny is that the issue with your idea is written in your own post, i quoted it for you. So you want to concede when you have no fun because your team is being destroyed? Well, that's pretty selfish in my opinion. Have you ever thought about the other coach's fun?
Say your opponent is a dad, full time job etc. He play hardly 3 games a week because he don't have time. He finally find some time, get on and is matched with you. Turn 6, you have 3 dead and 5 KO. You concede, cuz eh its no funz. Do you think that guy will be happy?
Or if getting destroyed and not much to hope for, skip turns after getting my players in a safe zone.
Maybe fouling with my star players in hope of having them send off, in case my opponent is a bad bully.
Still, we have to remember this sentence "Have you ever thought about the other coach's fun?" goes both sides.
Sometimes, and particularly in match making, you play against a smart player with some kind of Chaos team that takes pleasure in destroying your team. Sometimes he even doesn't care about winning the game, taking spps for later, or sometimes he's won the game already but continues clawpombing for spps, and fouling which doesn't even earn him spps. I feel this is someone who doesn't care about the other coach's fun. I don't want to play those smart guys, and understand concessions can happen in those cases.
In most casual games you choose your opponent, or/and can concede if you want (chess, heartstone...).
In BB you don't choose your opponent (you can choose your league, you can choose to stop MM as i do), you're not supposed to concede, but one can understand that asking to play for a bully's pleasure can be to much.