I suspect many of them have already left and moved over to WoT where there are no planes.
AH already has many of the features that WoT players dream of, bigger maps, no icons, better physics modeling, Development team with no bias, etc.
With WoT going live mid April, AH might want to offer a tank only alternative.
I guess it comes down to your point of view.
Do tanks exist only in AH to serve as targets for airplanes?
If that is truly your view then there is no need to change anything.
Or are they of equal importance to Aircraft, just a different way of playing the same game.
And if that truly is the case then a GV only arena is long overdue.
Put it on an island, put ports, task force's around the outside. Make it possible to do a Amphibious assault, as well as just tanks.
Build it and they will come.