OMG OMG OMG OMG!!!!!!!!!!!
I just accidentally discovered that room images do not automatically get readjusted to the size of the room they are in anymore!!!!!!
What does this mean exactly??? Well that means that ship modders can actually have a lot more details on the interior of their ships now.
Say you want to make a crew quarters/dormitory in an empty room. Well now you can, without having a system in that room.
Let me show you what I mean...
Here is a proof of concept I recently made. This image uses the following redone "room_oxygen" image.
Before AE this image would be shrunken down to fit the 35x70 pixel room where the oxygen is on the Kestrel, but now by making the image bigger we can add some details like this... Notice the back of the Kestrel?

The artillery was just something else I was playing around with, that's not part of the room_oxygen image.
So yeah.

Now you can have details even in entirely empty rooms.
Some other Miscellaneous things worth pointing out.
- The image will be "anchored" to the upper-left hand corner of the room it is located in still, so if you over expand the size of the image, it will expand toward the bottom and right. (Thus, why I chose to use oxygen.)
- If you want to use this method to add details to a custom ship you will most likely want to attach the room to a starting system, and a system that will not be replaced, so you have the details always. (although it is possible to do this with any system)
- Yes, images can "overlap", but I'm not entirely sure in what order. I'll hypothesize that the order is based on how the systems are listed in the .xml blueprints file. So this means that you can have one image replace another image entirely, when you buy a new system for example, (you could actually include the tiles instead of transparency to overlap the whole room) or you could have an image "add" details to the room (by keeping transparency and making sure none of the other parts will actually overlap in a weird way.
(Examples: You could start out with a crew dormitory and then replace it with a hacking system image, "sorry guys we need this room, guess you're sleeping on the floor."
)
- This would have all been great before AE, but AE actually complicates things a bit, since now you need each of the 14 different systems (not including artillery) to be assigned to a different room whether or not you'll be able to obtain them all. So there aren't really many "empty" rooms where you can do this anymore, tus why it is probably more useful for "custom" ships. HOWEVER, I would love to see someone add some tiny details to the player ships so that we don't have any empty rooms ever (remember that other system images can overlap previous ones)
- And I'm probably forgetting something, but that's all I've got for now. For anyone interested room tiles are 35x35 pixels and walls extend 2 pixels into the boarders of a room.
I took some inspiration from this image in my testing. Check it out it's kind of cool.
http://ftlonline.webs.com/Game/Ship_Map_Full.png