The X1 aircraft is comparable in size to a small regional airliner and can achieve a maximum takeoff weight exceeding 25,000 pounds with the help of four wing-mounted electric motors. The battery-electric propulsion system delivered more than one megawatt of power during the maiden flight.
That is not an option for islands or sometimes a train has to go the long way around, due to large bodies of water. Korea - Japan or something like Greece - southern Italy are interesting flights for example.