Not sure if you're still updating this... Is it possible to add an "autonomous" mode where it drives around on its own filling in any ghosts that it can, returning to a base site for refill when any product gets below, say, 10% of max?

Here's why:
https://factorioprints.com/view/-MNZWdWosuqr3vtaC2hD

I'd love to be able to go to map view (Big Brother radar gives a huge line of sight) and drop block outlines over the entire region. Then I'd send the construction train its edge and let it do its thing.

For an algorithm, I think the train could just drive forward, building out the ghost rails as it goes. If there is a branch, it looks forward and takes whichever path most quickly leads to another ghost.

That's a simplistic answer, of course, and there are complications, water being the most obvious. Avoid paths that end at water? Add landfill and rail ghosts until an existing rail (ghost?) is encountered?

What do you think?

So I had a look at this on my 1.0 game. And hmm, I like the idea but the code got pretty complicated after coming back to it a few times.

I might have another go, but a big part is actually figuring out those paths, since not a simple goto-station (isn't an ideal station to go to) and trying to programmatically spawn temp stations I kept having issues.

So looking at a partial solution, namely a way to let a player easily send the train over where it needs to be. Since humans seem to do a much better job at just seeing the right spot to go to.

Not sure if this is still WIP, but if the main problem is how to tell train next point to go, inspiration could be in the latest LTN placing temporary GPS targets (not stations) as the waypoints before reaching the distinct stations of the same name.

In other words, the LTN approach is proof of concept creating temporary train waypoint while not constructing and deconstructing station itself.

I have found this mod with other use case in mind: runing my virgin playthrough SE mod I would appreciate auto-reparations/replacements after meteor strikes all over the LTN network, without need to cover all the rails by robotic network. So alongside to auto-constructing of ghosts I would appreciate auto-repairing damaged structures (including rails themself) as well.