Is there already such a mod that compiles the unlockable costumes from the PS1, the Saturn and Nintendo DS "Deadly Silence" ports, as well as the ones included with the 1997 Director's Cut version?

The DS costumes for Jill (Stripper Cop), Chris (Ninja) and Rebecca (Cheerleader with a pom pom instead of the knife) in particular are quite something.

Could the costumes in the console ports/versions even be extracted and somehow made compatible with (and then modded into) the PC version to begin with?

Surely could prove an interesting challenge for modders.

"Porting" console-exclusive content to the PC by way of a mod or hack is definitely not unheard of - the PS3-exclusive "Play as the Joker" content for Arkham Asylum comes to mind.

Let's hope for the best.

it has already been done, the thing is there isn't a way to download them anymore, the mod scene is almost dead for these games, there is a discord for modding these games and maybe you could ask for a link but i'm not sure. I want to mod the games but everything has been outdated, tools that cannot run on win10 or is considered as a thread by windows defender, so i'm not so optimistic but maybe they can tell you where is a site to download mods for resident evil, i think you can try nexus mod or mod DB ... good luck...