The biggest problem with most ship interior ideas is that they need content to justify it. I personally find the idea of walking around inside your ship, but the walking needs to matter and be useful, not just aesthetic, or it's not worth the extra dev time.
But I think there is a real practical way to do it; multicrew.
Right now, Multicrew is very limited as far as actually being a crew is concerned. They give you a bonus pip, which is nice, and they can fly a fighter, but when I think Crew I think Star Trek or Star Wars. "Power to shields!", or "Maximum Impulse!", that sort of thing.
So here's the idea. Inside the cockpit, there should be control panels. The number of available panels a ship will have is the number of crewmates the ship can handle, plus one. So ships with 1 extra seat will have 2 panels, and ships with 3 extra seats will have 4. Here's an example with the Crusader, which has 3 extra seats:
What do they do? Each of these control panels can be connected to a ship subsystem, but only one subsystem at a time.
To swap from one subsystem to another, you need to exit the one subsystem and boot up the other, which takes time. In combat, you probably won't have time to swap at a single panel, so you'll need to have different subsystems active on different panels. So crewmates will need to run from panel to panel, know what's going on in each subsystem, and make changes rapidly and on the fly. On the Crusader, you could have two crewmates in fighters, meaning the remaining crewmate would need to run the turrets AND manage the subsystems, which means a LOT of running around! And of course, if there's any boosting going on, they'll get thrown around and knocked into walls, making things even more challenging.
This is the added gameplay from the walkable interior! Manevering inside the cabin under high g-forces would be a challenge, and they'd need to time their movements in coordination with the pilot to make sure they don't get thrown into a wall and pinned there for a while. On smaller ships with just a copilot, there would be no need to run, but only 2 panels, so they'd need to think ahead, instead, and plan for what the pilot will need.
Now, to make this worthwhile, each different subsystem control would need to have its own worthwhile bonuses. I've thought up some ideas for what they could do.
Shields
The Shields subsystem panel would look something like a combination of these two things. You would be able to see exactly where damage is coming from, and you could select portions of the shield to specifically enhance, reducing damage from that direction specifically. Alternatively, you could redirect power to force the shields to regenerate even while taking damage, increase the regeneration rate beyond the normal limit, or increase efficiency to reduce distributor draw, by looking for fluctuations in specific quadrants of the shields, and neutralizing them in real time.
Engines
The Engines subsystem panel would display the fuel tanks, the shape of the thrust, and the thermal vents. You would be able to redirect power in different ways; immediately after a boost, you could direct power to the cooling subsystems, allowing the next boost to happen faster, or simply reducing heat. Alternatively, the flow of the engines could be enhanced, increasing the maximum boost speed above normal. Or, you could redirect power to the lateral thrusters, increasing turning rate and strafe acceleration. If the engines are caused to reboot, you can vent the captured fuel and increase pressure to reduce the reboot time. You could even partially mitigate the effects of thargoid lightning to make it possible to escape!
Weapons
Weapons can be enhanced to provide short-term bonuses to specific stats. Fire rates can be enhanced temporarily, or the damage of the next shot specifically. Distributor draw can be made temporarily more efficient, or heat can be diverted to vent more efficiently. Gimbals can have their jitter reduced. All of these things have a cooldown period and have to be used at the right time for maximum effect.
Maintenance
This would be the fourth panel, and would be how crewmates could synthesize and repair. Unlike the pilot, they couldn't be interrupted by damage.
This would allow for walking around inside the cockpit, and make Multicrew a much deeper and more interesting experience.
But I think there is a real practical way to do it; multicrew.
Right now, Multicrew is very limited as far as actually being a crew is concerned. They give you a bonus pip, which is nice, and they can fly a fighter, but when I think Crew I think Star Trek or Star Wars. "Power to shields!", or "Maximum Impulse!", that sort of thing.
So here's the idea. Inside the cockpit, there should be control panels. The number of available panels a ship will have is the number of crewmates the ship can handle, plus one. So ships with 1 extra seat will have 2 panels, and ships with 3 extra seats will have 4. Here's an example with the Crusader, which has 3 extra seats:
What do they do? Each of these control panels can be connected to a ship subsystem, but only one subsystem at a time.
To swap from one subsystem to another, you need to exit the one subsystem and boot up the other, which takes time. In combat, you probably won't have time to swap at a single panel, so you'll need to have different subsystems active on different panels. So crewmates will need to run from panel to panel, know what's going on in each subsystem, and make changes rapidly and on the fly. On the Crusader, you could have two crewmates in fighters, meaning the remaining crewmate would need to run the turrets AND manage the subsystems, which means a LOT of running around! And of course, if there's any boosting going on, they'll get thrown around and knocked into walls, making things even more challenging.
This is the added gameplay from the walkable interior! Manevering inside the cabin under high g-forces would be a challenge, and they'd need to time their movements in coordination with the pilot to make sure they don't get thrown into a wall and pinned there for a while. On smaller ships with just a copilot, there would be no need to run, but only 2 panels, so they'd need to think ahead, instead, and plan for what the pilot will need.
Now, to make this worthwhile, each different subsystem control would need to have its own worthwhile bonuses. I've thought up some ideas for what they could do.
Shields
The Shields subsystem panel would look something like a combination of these two things. You would be able to see exactly where damage is coming from, and you could select portions of the shield to specifically enhance, reducing damage from that direction specifically. Alternatively, you could redirect power to force the shields to regenerate even while taking damage, increase the regeneration rate beyond the normal limit, or increase efficiency to reduce distributor draw, by looking for fluctuations in specific quadrants of the shields, and neutralizing them in real time.
Engines
The Engines subsystem panel would display the fuel tanks, the shape of the thrust, and the thermal vents. You would be able to redirect power in different ways; immediately after a boost, you could direct power to the cooling subsystems, allowing the next boost to happen faster, or simply reducing heat. Alternatively, the flow of the engines could be enhanced, increasing the maximum boost speed above normal. Or, you could redirect power to the lateral thrusters, increasing turning rate and strafe acceleration. If the engines are caused to reboot, you can vent the captured fuel and increase pressure to reduce the reboot time. You could even partially mitigate the effects of thargoid lightning to make it possible to escape!
Weapons
Weapons can be enhanced to provide short-term bonuses to specific stats. Fire rates can be enhanced temporarily, or the damage of the next shot specifically. Distributor draw can be made temporarily more efficient, or heat can be diverted to vent more efficiently. Gimbals can have their jitter reduced. All of these things have a cooldown period and have to be used at the right time for maximum effect.
Maintenance
This would be the fourth panel, and would be how crewmates could synthesize and repair. Unlike the pilot, they couldn't be interrupted by damage.
This would allow for walking around inside the cockpit, and make Multicrew a much deeper and more interesting experience.
(Needlessly cumbersome UIs just happens to be a particular bugbear of mine, especially in these days of small-touchscreen UI paradigms invading places where they do not fit, and I still detest most of the UI changes that came with with Odyssey -- your mileage may vary, of course.)