I can just see it now all the anti gun morons having a news conference to bitch about something that does not exist.
Technically, with the beauty of picatinny rails, just about anything is possible. In fact, someone could create sort of dual picatinny mount, sort of like those scope mounts for handguns that are independent of the slide. With an adapter you could mount one on a picatinny front rail of say an AR or something. Who needs a holster when your sidearm is directly beneath the barrel of your primary! j/k