As a note on YS206: I read that a bit differently. It doesn't mean you need to concede before rolling defense. It does mean that if you literally can't soak all the shifts of an attack (defense rolled yet or not), concession is no longer on the table. However, I could totally see a player saying "Yeah, I could keep fighting if I took a severe consequence... but I don't think this conflict is worth that; can we work out a reasonable concession instead?" - and that'd be perfectly OK in my games. Of course, the terms of such a concession would be rather less favorable than if they'd conceded before the attack (and thus before a severe consequence was on the line)... but it'd still be a concession, not a take-out.
This even goes for extreme consequences - but if a PC would need to take an extreme to stay in the fight, all that conceding will really buy them is that they're not going to die.