There isn't a jet in existence that's optimized for ultra-high capacity and short routes, and there isn't a market for one either. You can count on one hand the number of airports in the world that are seriously limited by number of arrival/departure pairs. Heathrow is #1.
Say I want to fly from Philadelphia to NYC, add more than 2 hours for getting to/from airports, and check-ins/screenings. But I can take a train in an hour and a half, and that drops me off in manhatan. I didnt even need to get de-belted, de-shoed, and throw away my sun screen and water bottle. And I wont be bumped off my seat because some senator doesn't like to book tickets in a timely manner.
humiliations aside, when I use to fly pittsburgh/philadelphia, i found that the train or bus was not a significant increase in time. The train/buses I could take and get off in the city centers, where as the airports added additional 2.5 hours time. but when you factored in waiting 30 minutes to get my baggage from baggage claim, time spent sitting on the runway, time having to show up early to get checked in and numerous security lines, it wasn't that much savings in time. I was paying about 300$ for 1.5-2 hour savings in time for a much more stressful experience.