I can’t see it being free. If you look at Star Citizen, their concepts are pretty comprehensive with planned layouts yet it still takes a year to go on sale - and they have a pretty well established pipeline now.
However you look at it, interiors isn’t a side project. The only way it would make financial sense is to be a paid expansion. And people are going to want more from an expansion than just somewhere pretty to look at.
This is an excellent point to make but there are 2 things to consider about this because 'Ship Interiors' is a very broad term which can stand for a lot.
1. SC is ... kind of a scam one way or another. 700B and 12 years ... ? I think think you could have actually established a RL space colony with that time&money XD
(But let's not dwell on that)
2. There is many ways to do Ship Interiors.
Most ppl hope/imagine actual fully modelled Interiors like you see in the YT-Videos. (That would be absolutely GLORIOUS ... but is it maybe too much to ask ...?)
Those would 100% have to be paid and would also be an insane amount of work (maybe even more than actual_atmo-Worlds)
But there are simpler, cheaper (but still very good) ways to do them.
If I was in charge at FDev, I would probably go for that route.
E.g. Just 2-3 rooms per Ship.
And they wouldn't even have to be permanently acessible but only when the Ship is stationary.
Furthermore, I would utilize an elevator as a hidden loading screen and if you really wanted to, you could be even cheaper by not having any windows (that one would rly suc tough).
HOWEVER:
Then they could very well be free
