Depending on if it's possible to scale the 'random stuff' plots to fill an arbitrary surface with stuff, you could have internal plots work by designating the walls, floor and ceiling of an internal space of sufficient size as a plot, then filling it with random based on what kind of plot the room in question is being.
There's the effort of designating flat surfaces for sticking stuff on, there's designing a random placement system (ideally would steal whatever one of the two? mods that randomly place stuff do), and populating a random list of stuff to place.
You wouldn't be able to have a counter line up with the hallways in the Castle, for example, but in theory, you could have a doctor's office that fills the available wall and floor space with doctor-themed greebles.
To do that I think you'd need a bunch of lists of set pieces classified by plot type and tier and by placement rules:
- posters, lights, some cabinets or plot-specific greebles go on the walls around this high.
- Some furniture goes against the wall if possible, some goes in the middle of the floor area, there needs to be enough room to walk around the furniture, this side towards the door.
For multiple tiers, a combination of cost of the item in question and how full the available space is; Tier 1 would be sparsely decorated with only cheaper equipment, while tier 3 would fill the available space and have more expensive stuff.
For indoor agricultural plots, there are the planters from Grey Garden that could be used; possibly needs significant power to run the grow lights. Perhaps an aquarium, or a hydroponics setup, presuming that someone's willing to model up something appropriate. Nice thing about most indoor food stuff, you can usefully abstract the different kinds of stuff you can grow as a shelf full of stuff that doesn't need to be connected to any other stuff, and thus the placement requirements would be 'is there enough room for an NPC to walk between the shelves'.
A nifty kind of indoor food is mushrooms; there's brain fungus and glowing mushrooms, both of which aren't technically food, but rather ingredients for medicine, but would be a plus to have a steady source of, grow quite happily indoors, and can be liberally sprinkled on any available flat surface (for brain fungus), or any horizontal flat surface for glowing mushrooms.
There's a mod that has a replacement model for the stock vendor stalls that is cut down short enough to fit indoors and has added store-specific greebles that could be used to have one of each kind of vendor indoors.
For indoor residential, possibly fastest possible thing would be to just place a random bed down and call it done.
