The player has a set vision range. Let the player see farther than that if they have a weapon with a range farther than that, matching the range. So up to 20 with a sniper rifle, but only while the sniper rifle is the active weapon. It would make sense if it only worked in the direction the player is facing, and maybe even only while "focused". Right now in underrail, sniper rifles are the weakest gun type, so it's a balance concern, but it would also just be a really neat feature imo.
Also, it would be good if there was an option to have the player change their facing direction without having to move. Kinda bugged me in my runs where I have good detection; you want to be facing any incoming stealth enemies.