I think either the Vickers or Maxim could use a new ability to separate them from the rest of the HMGs.
They are the two oldest designs in the game, both being pre-WWI designs, so I think their use should reflect that old philosophy.
An early MG tactic was to use them as light artillery, firing in an arc at long ranges to barrage and harass enemy units. This could be done as an ability for either unit that allows them at Vet 1 to fire a “suppressing barrage” that does light AoE damage and suppression in the target area.
Another ability idea could be like the strafing fire ability that the Centaur has. The MG fires a long burst sweeping from side to side damaging and suppressing everything in a cone in front of the gun.
Another active ability? No, god sake. Maxim is unique MG that need to use ability to do mg work, while other mg do it by default. I don't mind it gainst new ability, but first we need find decision about battle stats and preventing spam and after that search new abilities.
From what was said before - IMHO longer set-up time could be used as decision. Increase arc of fire to in-line maxim with other mg's. Because it's very odd that mg with weakest supression have narrow arc. Narrow arc was design from old times when maxim was instasupress platform with fast set-up time. These times are gone and arc of fire need to make normal.