I was thinking that maybe there should be an attachment point for brass catchers, ghilie wraps, and side saddle shell carriers, and the like, although I’m not entirely happy with any of the names I’ve thought of for it.
Brass catchers could be used to store rather than eject cartridge cases for handloading.
Ghilie wraps wouldn’t offer much of if any improvement to the statistics of a weapon, but offer good enough camouflage that some people would prefer that they not just be cosmetics, but actual items that need to be obtained in-game and take up and attachment slot.
Side saddle shell carriers can hold a number of shells or cartridges to be loaded more quickly into the weapon. (note: shell carriers attached to the stock, the sling, or worn on the wrist are not the same as side saddle carriers, and I am not suggesting that they would occupy the same attachment slot as a brass catching attachment.)
Maybe dust covers and stripper clip guides could also be available for some weapons (though on other weapons the dust covers and stripper clip guides should be integral to the receiver, not attached to it.)
Some of these attachments might also add different types of attachment rails.
Perhaps carry handles could occupy this attachment slot as well. Carry handles could be useful for hipfire and for vaulting over obstacles with the weapon out.
I really thought I would have more to say about this with how long it took to explain that suggestion for lockwork attachments,
especially explaining to a certain someone, who I still am unsure whether they genuinely had difficulty understanding the post or were more interested in making up something to complain about than in evaluating anything I was actually suggesting.