Hey! probably a toggleable setting, but I think it would be cool if turrets also downgraded in quality if they are inactive for too long, kind of like they need practice to maintain their skill or something

Good idea! I’ll look into it. Do you have any suggestions for how long it should take?

A very long time, I think.
Like 2-5 hours, imagine your legendary turret downgrading.
It's okay for your working and evolving towers to downgrade, but that turret that you actively grinded for downgrading? That feels bad.
I can imagine maybe multiple techs that would limit the min downgrade: normal / common / etc up to legendary (or mythic if that mod is used). If possible.

How would it interact with REAL quality turrets, though?

Sorry? wtf is a real quality quality turrets?

Turrets who have their quality from being built with quality, rather than kills