I remember that we, at least for a while, used to have textures for the see through lingerie and the lacy underwear. I think I even still saw them in the game files a while ago, but it seems they are no longer being used. Is there a reason for that, or are they just temporarily out and will come back?

I dont think so, it was an option for helper girl in first game though

Out of curiosity, why were the textures removed(I mean the ones for the character creator made ragdolls)?  

As far as I remember they were even fully colored already and looked fine on the ragdolls too.

Not sure what you mean honestly

There used to be on-character-textures for those two items displayed on the random characters if you had the corresponding item equipped(in Conquest). 

i.e. If you equipped them, they had clothing textures on the random characters's avatar/ragdoll(on the inventory screen for example). - Just like armor and other costumes do(The Mantle for example.)I, specifically talking about the random characters here, not story characters.

If I recall right, they were there around the time you introduced the avatars/ragdolls for the random characters and vanished a several itch versions later. 

However, at some point the clothing/costume textures for those two suddenly stopped displaying on the characters. 

The only real issue with those two I remember is that the underwear was using the See-Through's texture and vis versa, which is why I was wondering why they are gone/if they would eventually return.