You are right about the MKII, The standard velocity of 22 LR is around 1100 ft/s which is just below the speed of sound, which at standard conditions is 1,126 ft/s. The super quite capabilities of the VSS is complemented by the Subsonic ammo it uses. No other gun in the game uses this type of ammunition.
(google info about common 22 LR Velocity's) "22 LR ammunition is rated at 1,070 ft/s (330 m/s). Most standard velocity ammo has a bullet weight of 40 gr (2.6 g). Standard-velocity cartridges generate near or slightly supersonic velocities."
So something with the 22lr needs to be tweaked to realism when suppressed. Adding a variation to each caliber like the 12ga in game would be awesome. They added Slugs, Rubber Slug, and they already had 00 Buckshot but I would love to see variations of other ammo! I know we've had Tracers for awhile which is awesome to see but maybe add hollow points or FMJ too! I don't think incendiary rounds would really benefit the game right now but I could definitely see others being a benefit. The possibilities are endless but the dev team is not Lol so we just have to be happy with what we have but hey! We are in suggestion forum after all.
Reply to what you said about the Gas systems. Correct me if i'm wrong but this is a game after all so I don't feel like the gas system of each weapon is a mechanic in DayZ. I am no game developer or coder but like the tracer and non tracer rounds in game the gun will shoot knowing which round its firing. This can be seen if you stagger Non-tracers with tracers in the same magazine.
I have to admit I would love to see the Welrod 9mm in game as well!