I know this has probably been discussed a thousend times over, however i wanted to give an idea.
What i'm proposing isn't any fancy holster system but rather 3d models inside the vest model.
There are many vests that have "built in" things like modeled STANAG magazines, GPS or pistol magazines that stay there despite you have them in your inventory or not, so why not adding a pistol model inside the holster as well?