FOSS gamedev and creative worlds

I have this idea of creating large vehicles like cars, lorries, trains and what not.
I see that the carts mod by PilzAdam supplies the cart as an entity. My understanding of an entity is that it has a separate life compared to "proper" nodes.

So basically (as I understand it) I have two choices:
1) Needing the ability to create build-able entities which when connected can create a larger vehicle.
Combined entities would take up maybe 100dreds blocks of space.
2) Moving (possibly) large amounts of blocks around to create e.g. a train.

Also trains cannot run on a schedule because at least entities are disabled once no players are near.

I'd like some opinions and ideas and perhaps indications if this is at all possible or if this kind of transportation would require engine changes of an unfeasible scale.

I think it could be really fun to create trains using normal nodes and have them move across the landscape.

My idea, not sure how feasible it is:
Define a special "vehicle base" node. Whenever a node is built to a vehicle base node, it is added to a list. (nodes can also be added by building them to a node on the list) When the vehicle is supposed to move, the nodes are all converted to entities in the same way falling gravel/sand are, and are connected to each other and moved as a unit. The player is connected to the vehicle base node to steer it. When you want to edit the vehicle, the positions of the entities are rounded to the nearest node and the entities are converted back to nodes.

This is actually in the long-term section of the TODO list.
http://dev.minetest.net/TODO