Great battery life and linux unfortunately are a hard task and linux support is often spotty for consumer devices.

Sticking to used business hardware is usually a good start, but you should check for compability issues nonetheless.

Used t490 / t480. Can you elaborate on the “heavy limited by space”?

If someone was willing to invest into building and maintaining infrastructure there would be no need for this concept, but that’s a political issue. The idea of this concept is do make the best of what you have.

How would traffic pass each other? You would be stuck with the same issue as normal trains.