Electric aircraft for shorter trips instead of trains. The battery energy density still needs to improve somewhat but that is happening. They’d allow for serving more direct (point to point) routes than trains as the infrastructure cost is so much lower than laying and maintaining tracks. Rail serving high volume routes still makes sense, especially while electric plans remain relatively small.
I might be wrong but this seems like a very US-centric idea. For most of the developed world trains fill this need very well, while the US has had problems with their rail network for reasons partially based on geography, partially based on population density, and partially based on their own fault. I think this explains it pretty well: https://www.youtube.com/watch?v=mbEfzuCLoAQ The solution is not aircraft, the sol…
That leaves most of Asia outside India/China/Korea/Japan, and pretty much all of Australia/Oceania, Africa, the Middle East, and the entire New World.
I would love to see high-speed rail take over the world, but there's a lot of sparsely-populated places out there, and it makes sense to investigate technologies to support them.