Airline pilot here, you'd be surprised how often I'm at max takeoff weight. Especially during the summer. This looks like you'd cram like 40 more pax on board which would for sure cause all sorts of weight issues. The newest configurations have added about ten seats and that's already pushing it, but I'd imagine they'd want to try this on the short haul routes as you can't take the same fuel when dealing with high loads.

You have to understand that everything in aviation is stretched to it's theoretical max already. Fuel savings of 3% is airline dominance. Overselling flights for load factors gaining an extra 2 percent? Industry standard. Building schedules for crews down to the minute so they are technically illegal if something causes a delay? Worth it. But you can get a ticket to fly a thousand miles for 80 bucks on a low cost carrier, so the rest have to squeeze too. If they haven't implemented something like this, there is a glaring flaw logistically or legally.