Perhaps we will eventually have a 500 seat twin-jet. Future engines will be able to produce over 150,000lb thrust and there will be passenger growth to make this viable.
.............and then there is the flip side; it arrived too late and with too many modifications to airports required for broad usage......it costs a bomb to keep in the air.......point to point flying is preferred by the public..........and add to this flight frequency with smaller aircraft that are more fuel-efficient is preferred..........no, we are unlikely to see super large aircraft again in our lifetime.