The work on the "Standing chair" is all fine and well, its been around for a while.
The issue is whether the airframe as it currently exists (and as we're talking FR it'll be 737-800) can accommodate the evacuation of the the increased number of passengers, an extra 30 in this case (5 extra rows x 6 "seats" each), within the 90 seconds allowed using only half the exits. And, who's paying for the recertification?
I'm sure there's someone here who can (and will) correct me if I'm wrong, that 800 is certified for 189 pax. But when Boeing pushed for the 200+ pax 739 they needed to add a door on each side to the design to accommodate evacuation times.
JAS