Actually, you know what might be better than this active ability, then?
If the Vickers instead got an active "Artillery" AOE ability, with approximately the same functionality as the Bofors' Suppressive Fire volley. This would allow them to suppress an area at range, but avoid any of these supposed "issues" with having a temporary range increase.
It would more closely matching with the "historical" use of the Vickers, and could conceivably be allowed to fire further, and perhaps even through/over shot blockers (Though this would obviously be subject to scrutiny). It also echoes the function of another British unit, the previously mentioned Bofors, but is otherwise very unique among HMGs.
Does the Vickers have an animation/blend that allows it to point "upwards"?
This would actually be really cool if a modder can try and make this happen. Might be a bit difficult to balance with how strong to make the suppression and how fast it lands but I'd be game to see it attempted!