In the upcoming updates, there should be a new cord item that you can attach to a minecart and a building. A tripwire hook or something looking like that can be placed on the chosen building, in which the cord can be tied to. When the minecart goes, the building goes with it like a tow truck. Obviously if the minecart stops somewhere between two blocks, the program would round to the nearest block and snap it there. Of course, there would be parameters for options, such as, include entities, only connected blocks, choose dimensions, etc...
Would there be a blacklist of blocks that wouldn't be moved? If not, how would the game know to move only the house you just built and not the grass next to it too? I like the idea, but I need a little more information.
While this is a neat idea, I don’t think it be possible, at least not how Minecraft is currently coded. I may be wrong, but I’m pretty sure structure blocks are designed to create blocks. The only way to make an object move is to create an entity (not a block), and a single moving large entity would cause a LOT of lag. Multiple entities and the game would probably crash. I don't even want to think about what would happen on large servers.
Besides that, this idea would make minecart with chests/furnaces/TNT redundant. Why create a minecart with just one chest when you can attach a minecart to a platform with as many chests as you want?
Rather than towing buildings, it would be better if the buildings were carried on top of the minecarts, with each minecart being able to carry up to a 3*3-block square on top of it, and with an additional height limit, similarly to how premade houses can be transported by trucks IRL, but with a lot of minecarts:
This would make defining the limits of the structure being transported a lot easier, and wouldn't look silly.