I have seen that mechanical assets have been rejected by the devs Trello page this is understandable but disappointing for numerous reasons but I have a way around the need for traditional rails for trains maglev technology. This would allow players to make constructs that are powered only by batteries which would allow for simple transportation that are recharged by renewable energy if the DU devs decided to include that form of power generation but more importantly will be a way to move constructs on a track without having the construct physically touch the building it rests on, which would be much lighter on our computers as there would be no need for collision simulation. The use for Maglev engines would not just be limited to trains but also elevators that can move sideways, space elevators, ship catapults to launch ships like in Battlestar Galactica and large mobile launch platforms like that used by NASA for their spacecraft.
In summary, Maglev engines could serve as a compromise between the players need for mechanical assets to make moving parts and the devs concerns for game performance by letting players use a contactless rail system.
I hope I made my idea clear let me know what you think.
Dark_but_Good