I find the plating system, and its derivative, the interiors system really awkward.
I can almost never plate just the objects I want, because the plating is placed sort of like blocks outside the hull. So if there's a 90o interior corner, the entire corner has to be the same sort of plating. Also, this causes problems with non-cubic blocks - I've had ships with slopes on them, and I can't make the ship symmetrical because the sides of the block which get picked up by a given plating placement changes depending on the orientation of the block.
The awkwardness of this system is ultimately what's causing the complexity of the interiors system - if we could just paint plating onto polygons rather than all polygons the system decides are adjacent to a block we put down, we wouldn't need an interiors system at all (just more kinds of plating) and wouldn't need this upcoming oddness where we define an interior and then manually fix all the areas where it got it wrong. (Like over doorways, as shown in the demo for the "fix interiors") feature.
Plating being set on adjacent blocks is also, of course, the root of the "placeables strip plating off of nearby walls" problem.
Additionally, because plating can only be set on structural blocks, we end up having to hide utilities, cabling and vents and whatnot behind solid, meter thick structure. I end up having to make ship decks 4 meters thick because of this - 1m of ceiling, 2m of room to allow for different utilities to go around each other, and then 1m of flooring. Since my decks are only 3m tall, this means I have more solid metal in my ships to allow for utilities than I do living space!
I don't know what the technical restrictions are, but it seems to me that moving plating to be a property of the block (per-polygon) rather than being based on an invisible, adjacent block would be a big win: it would solve pretty much all of the problems above. Additionally, by allowing us to plate certain other kinds of blocks and placeables (for instance, the underside of the "cockpit" placeable) we could put cabling in 1m thick ceilings and floors and just plate over them, substantially simplifying the process of ship layout, and minimize the huge amount of bloat created in ship designs to leave room for these features.