Here's an expanded idea for how Interiors could be worked into Ship Engineering, offering the sorts of scale that might be needed to make it all worthwhile.
Ship Interior engineering
The problem with Ship Interiors is simple from a Developer's standpoint. The ROI just isn't there. Look at features like Colonization: For the first time, we can actually tell EXACTLY how much time a new feature generates. In the first week, about a billion tons of commodities got moved for colonization, according to Galnet. With 792 tons of cargo per load, that's about 250,000 hours of player time, in the first few weeks alone!
By contrast, something like ship interiors - even if you added EVERY feature people have thought of - would only give a bare fraction of that. Internal repairs, salvage, cosmetics, crew...all those things are things you do very infrequently. Repairs, for example, I typically spend maybe a few minutes a week doing. Salvage is similar. Cosmetics, also similar. Even if I did EVERYTHING that interiors offer, I'd be looking at maybe 15 minutes a week - compared to needing to invest at LEAST 10 hours a week to finish a large station in the required four weeks!
So you can see, the ROI just isn't there. What is needed is a large feature, something that interlinks with other aspects of gameplay on a broad level, something that can be used constantly and indefinitely.
But as I thought about it, I realized...we already have a place that's ripe for expansion.
Engineering.
After all, even though the current engineering isn't BAD, it's also not exactly something players dream of, you know? It's a necessary hurdle you need to get past to play the game, it's not really compelling or fun in its own right. At best, you might think of new builds to try, but even then, the actual engineering part is secondary.
I think that Engineering could actually offer the sort of content needed to make Interiors worthwhile - IF it were implemented correctly.
Nuts and Bolts - Tinkering
Here's the basic idea. We already have examples, in Odyssey, of being able to cut open panels and see assorted materials arrayed inside. This would be the core principle of Engineering 2.0. Every module would have at least one panel that could be opened, to see the stuff inside. At a basic level, they'd all have an energy input, and an energy output. Between them could be placed a variety of different modules(engineering components), which would modify or change the energy flow.
For example, you open up a hardpoint's control panel. Inside, there are a bunch of 'G0' manufactured materials. You can pull them out, and replace them with G1 manufactured materials, giving you G1 engineering. Or, you can replace them with G5 manufactured materials, giving you G5 engineering. Human-made materials would be very consistent like this; you put in the required materials and you get the desired output. Engineers would do this for you, if you wanted them to, but you could also do it yourself.
Now, the tricky part here is that every engineering material should interact with every other engineering material, in a predictable and somewhat consistent, but also unexpected, manner. This would not always be as simple as, 'insert G5 material, get G5 result'. Sometimes, you might instead find that a G3 or G1 material enhances the power of another G5 material as much or more than using a G5 material there would. For example, putting a Heat Vane directly after a focus crystal, could multiply the strength of both. These are the things Engineers would know; that you could get the same engineering effect for a fraction the cost using these hidden synergies. But there would be more synergies than this, ones even the engineers don't know. But the only way to find out is via experimentation and tinkering.
This would also be how different effects are achieved. Combine the right materials in the right order, and you might get more ammo, or more damage, but never both at once.
Then, there would also be the non-human materials. These should be much more unpredictable, and even somewhat randomized, based on their source. Moreover, they should be ways to MODIFY other components, not be used on their own. For example, Iron could be used to enhance the integrity of a human component. You could take a chunk of iron, apply it to, say, a Heat Vent, and the heat vent is now more durable. But iron would also have other effects, hidden effects, based on where the iron was sourced. Iron from one planet might have some impurities that make it better or worse, or give it special characteristics, or make it work particularly well with one type of component. It would always do what it is supposed to, but it would also have additional features, hidden features, that must be discovered.
What does this achieve? It gives actual gameplay value to things like Exploration and Exobiology. No longer are they just about credits; every new planet you visit might have some new roll of the dice that makes the engineering materials sourced there incredibly valuable.
These effects could be discovered via a science lab inside your ship. In it, you can run tests and experiments on these materials to attempt to find their effects. For example, you might expose it to high heat for a prolonged period of time, and see how resistant to the heat it is. Or you might submerge it in acid, or electricity, or any number of other effects. This would take IRL time to do, so what you might do is go home(to your ship), start a bunch of experiments, and then go back to exploring for a bit, knowing that when you return, you'd have new data available to you. Worst case, this would at least enhance the value of whatever samples you have. And any useful effects, you could bookmark, so you would slowly build a catalogue of planets with useful effects, so you could return to find the materials you need.
However, planets should slowly be 'used up'. A planet that starts out plentiful with materials should reasonably be depleted over time if too many players are going there and harvesting everything in sight! So players would be encouraged to find their OWN harvesting grounds.
Summary
I'm not going to lie, this would be a pretty major rework of Engineering. But, as far as I can tell, a fairly major feature is NEEDED to justify the existence of Ship Interiors. And once they're justified, you could THEN add all the other neat things people want from them, but which aren't enough on their own to justify their creation! Repairs, crew, salvage, all that stuff could be added in tandem, making interiors the sort of fully-fleshed-out feature a significant enough pool of players could want!
