Whoa, this is damn quickly going overboard. Punitive repair and refueling costs again ? For the love of god no. Those were gamebreaking at one point and are fine where they are now.
Yeah, I don't understand why that was brought up, I am very much against that. Please don't interpret into my OP a wish for the game to be more punishing.
For me, the meaning behind the 10% loss on ship sale (and likewise on module sale) is that you don't just buy and sell your equipment on a whim in reality, either. It's not so much about punishment but about introducing a better sense of ownership. "This is mine and I am not giving it back" as opposed to "I temporarily deposited 10000cr to borrow it". Well, I have to admit engineer mods already do that, so there's that.
(By the way, 10% loss is very light. Usual figures for that in many games are more like a 50%-80% loss.)
Now for experimentation, I am in favour of a time window during which you can return any item for free, let's say 2 hours actual ingame time, enough to go out and seek (for example) a couple of fights to get a feeling for how a particular loadout plays.
I used to be ok with the idea of module depreciation even when others are annoyed by it but recent changes since it was last suggested (1.4?) have made me change my mind.
I own many ships, pretty much all of them bar the Cutter/Vette actually. Most are in specific loadouts, combat, exploration etc. Then came 2.0 and 2.1. Balance on its head, silent running is all but gone, railguns are no longer as viable, SCB's are no longer the way forward, other weapons got nerfed and buffed and I'm sat there with 25 odd ships that I need to re-configure to use.
Thats kind of a massive expense especially when we consider ships like the Corvette which prior to the SCB change could have been stacked with 2x 7A SCB's, thats 2mil in losses right there on one ship with one module change. This potentially massive expense every single update which is completely out of my control and could be as often as 4 times a year isn't something I really can agree with.
This is compounded now with Engineers as anything that gets modified like weapons can be nerfed meaning not only do you need the money to cover the 10% loss but you need time and materials to re-engineer the new module/weapon. As such I think having standard modules have a 10% depreciation is a bad thing unless there's an amnesty after updates or something to help us when FDev change the balance as dramatically as they have in the past..
My idea is that with module storage, when you replace a loadout for any reason, you don't just typically sell it again. You put it into storage for later use. Of course this requires said storage to be generously large, which I kind of silently assumed in the OP. When changing a loadout, unless you absolutely never ever want to use an item again, it should become a no-brainer to keep the equipment in the bank.
Especially with engineer mods, storage will probably be the norm, not selling. Just this week I switched out 3 guns on my Python, I moved them over to a different ship as storage (yes, a very clumsy and risky workaround), because I don't want to lose the mods (Phasing Sequence, I like my lasers blue) on them.