The current ore carts work as player vehicles. I was thinking it might be interesting to add a second type of ore cart that works like a chest-on-wheels. They would need to be placed on the tracks next to a player’s cart, and the player can then get in and pull the whole train along with them.
Maybe limit it to 5 carts total, with some fraction of powered rail required in order to move loaded carts uphill? (perhaps 1 out of every 4 rail nodes would need to be powered?)
In some ways, this would perform the same function as backpacks, but with a much more limited scope. Also, it would encourage players to build more rail infrastructure than we typically have been seeing in the game. It might also encourage players to be more thoughtful about their mine layout, so they can more-easily move materials to the surface.
but, as to players building better mines with rails, I dont think it will happen. This is because to mine well, one needs to travel vertically. Rails are not built for vertical movement. it requires building a 3×3 mineshaft, with a spiral, and 2 rails for every vertical node downwards. In a game where steel is expensive and might be the very thing you are mining for, this does not make economic sense to do.
Now, it would be VERY different if ores spawned in large rare clusters, near the surface. Then, you would want to build a horizantal mine, and carts would make a lot of sense.
Still, I think that adding minecarts would be a nice way to have automated transportation of people and goods