Current hardware is capable of handling such a sim, IMO.
When flying the Hog, the CPU is busy with : flight, avionics, weapons, AI, mission / campaign ( and anything else I may have omitted )
When driving a tank, the CPU would be busy with much of the same, if not less. You would not be flying the Hog and driving a tank simultaneously.
Of course, compromises would have to be made. The terrain looks decent at altitude, but it would look terrible ( by today's standards ) when driving a tank. Some additional graphics routines could be employed to spice up the visuals when on the ground, but that would steal development time from new aircraft modules which just 'fit well' with the current terrain.
Personally, I would be very happy with a study tank / Tunguska / e.t.c sim on the current terrain. ED just need to:
a) have the desire to broaden their horizons beyond aircraft simulation.
b) have similar military contracts / detailed information for tanks.
c) determine whether the market is there to make it a viable project.