Almost all primary weapons in the game have a merc which uses them as default. The exceptions are:
BR-16
Fel-IX
I heard that PDP used to be on Aimee. Fel-IX and MOA are very similar and I don’t think they will add another heavyweight sniper now that Vasili and Red Eye are in. So probably no Fel-IX merc, although it IS strange that Vasili is the only merc with two unique weapons. I guess there are many sniper lovers in Splash Damage.
What could possibly be the BR-16 merc ? Stoker is going to have Timik. It’s a bit crazy, but maybe Turtle ? I can’t imagine Turtle with shotguns because they would be utter crap from behind a shield.