This suggestion will be about British firearms I would like to see in this game.
The STEN Mk1 is a variant of the STEN that was used in relatively high numbers during WW2. The unmodded version had wooden furniture, folding grip, and flash hider.
There is also the STEN MkV which had wooden furniture, grip, and a bayonet lug. It would be nice to be able to actually equip a bayonet on it if this was added to the game.
I believe these variants should be available in the tech tree, with the Mk1 foldered with the Mk2.
The devs also have a tendency to put prototype weapons in the game, and the Sterling SMG was being tested during the later stages of WW2, so that can be a possibility as a premium/event/gold order.