Some type of rail / monorail
It would be awesome to have some track bound form of transportation on planets or in space. Possibly in the form of some kind of monorail (maglev style) or some other kind of rail system. This would allow for ground bound passenger and goods transportation along defined tracks (to connect different outposts etc.).
I know that there already are mods for this and even a train based on vanilla parts using tires but it would be great to have a non-hacky way to implement that.