I had two ideas that I think would nestle perfectly into this mod, which I haven't stopped using since I first found out about it.

1. The title practically says it all, the concept an interior space with an outlet on each side, and maybe a second tier with 2 on each side. Ideally this'll allow for compact turntables, changeovers and/or locomotive and car storage.

2. A freight elevator allows you to access additional floors, possibly in lieu of Recursion being the explanation for its function. Aesthetically, I'd recommend removing the corrugated roof on structures with multiple stories, and just have it capped off with black flat top to visually communicate that it's a multiple story structure.

As much as I'd like to implement your first suggestion, and as often as it has been suggested before, it's unfortunately completely impossible to mod in, and it likely won't ever be possible. You just can't mess with trains in that way.

As for your second suggestion: If I were to add multiple floors, I'd rather make them basements instead of higher floors, but given that recursion is already a thing I don't see the necessity for basements.

I think alternate floor would be better than Recursion in my opinion. Its all the same building for one so when destroyed all floors are lost forever, and it can be something you upgrade your structure with from the inside with some sort of "add a new level" option and a chest there that requires x amount of resources in it to enable the new floor. Access would be at the back of the factory in the center where nothing usually connects at.

I tend to disable recursion after all, cause it feels a bit silly. Though, seems to be broken now. (made a post for it)

Hey MagmaMcFry, I love this mod (I think I've said that before). The train thing probably comes up more than I realize, but I thought of a possible angle that could maybe at least help: Can Chest Connections be made to connect to stopped trains if the train is right next to the Factory? Could even be a research point, and if it works, maybe a huge FactoryBuildingMk4 that would have connections that line up with two or three train cars. Just a thought I had. Thanks!

There are other mods that make this possible already, for example this fine mod. You can connect a factory building directly to the bulk loader and it should work as intended.

I don't know how possible it is. . .add a basement expansion mechanic.

Basically, you craft a "stairwell" that can only be placed within another factory, that functions as the "door" to the basement. Perhaps place the stairs leading back up in the same relative location when that floor is created. The stairs would cost the same amount to craft as a regular factory, but if possible add the restriction that the size of the basement, must match the size of the original building.

Bonus points if you could allow pipes to feed other pipes above/below the current floor.