MoM design would end up roughly B762-sized
In all econ that was 260 pax. If you added a business class, which would have a fixed bulk-head, what would that create? It would depend where the bulk-head was, of course, and depend on the routes; but that would be quite a bit larger than B757/B737-900 stretch.
Problem is the economics of routes change very fast and the time frame from concept to first line flight is many years. Every day the future is getting more difficult to predict e.g. A380 in a world where perhaps the B747 is a dying breed and A340 is gasping for breath already. B787 A350 B777, perhaps A330 derivatives seem to be changing the world. Was that foreseen at concept time for A380? That does have a role to play, but can it achieve what B747 achieved?