Yes, many mission types could benefit from this. Like City Life for instance, by default the game would allow civilians and criminals to conceal pistols/machinepistols. This would also be good for a mission type me and my clan are devloping called "saboteur" where one team of soldiers defend targets in a city/town (Agia Marina for example) populated with AI civlians in which one civilian-factioned player has a pistol, a silencer, and some explosive chargers, problem is that the civlian "Saboteur" in ARMA 2 or in current ARMA 3 builds either has to have a backpack to store the pistol (which makes him look different from other civvies, ruining his cover), stash the pistol somewhere like a car until they need to get it, or just walk around brandishing it. The pistol holster option would fix the issue.

Holstering should be in the game. Upvoted!

It would certainly be nice to have. But it's covered by #3828.