Airships................
I'm not a physicist, but it seems to me that if you devote all your (on-board, stored, ie fuel) energy to thrust, and none to staying in the air, there's a gain somewhere.
So who needs to go to New York at 500Kts instead of at 120Kts?
Time for a book, film, meal and a zizz....perfect.
Modern materials and design, along with next generation thrust generation , could produce a superb, economic and safe vehicle.
Couldn't they.....?