I would love to have modular warehouses where you could build a base level and then just add modules to increase storage. There would be one entrance but you could add on in any direction, except maybe down unless you excavate.

I saw another Mod Idea/Request regarding warehouses storing multiple types of food, resources, manufactured goods, etc. A modular warehouse could potentially provide that and avoid manufacturing stalls in the same way the original warehouses did. My thought is that each expansion of the warehouse would hold a different type of good.

In a way, we sort of have this already, in that you can build multiple warehouses and create a "mega structure" of warehouses but that requires a bunch of building and each has its own entrance. The concept I am envisioning would have a single entrance and not require building platforms to get to higher levels (Maybe you would have to unlock platforms before you could build vertically?). It would also have a footprint that would only be as large as the base level. This means you could conceivably have a 1x1x16 warehouse, though that may be a bit extreme, probably a 2x2x16 would make more sense. You could also have a 16x16x1 warehouse if you wanted to expand horizontally. This would give you capability to expand storage in multiple ways and squeeze storage into nooks and crannies.