As a fan of the GV aspect in AH (both driving and bombing them), I would love to see more GVs in general.
On the topic of Tank Destroyers (Marder, Jagdpanzer, JagdPanther, JagdTiger, M10, ec.), I would rather see the regular turreted, closed top tanks first-Shermans, T-34s, Chuchills and Cromwells. There has been a call for M-18 Hellcats, but the problem (as I see it) with American TDs (or the Marders, for that matter) is their open top. Since this is primarily a flight sim, all you would need to do to stop a TD advance is to straffe the open top and that would be the end of the TD's offensive. Although with the trees the danger from aerial straffing attacks diminishes, I assume that the HE modeling in AH will stay the same, and all an enemy tank will have to do is airburst one of their HE shells on a tree turnk above your turret to get the same effect (Flakpanzers can already destroy their own main guns by shooting the roof of VHs when they spawn).
With the German Jadg and Soviet SU series TDs, the problem is more of aiming the main gun since they don't have turrets, and require using the driver to aim in the general direction (an option for HT would be to have hull rotational control available from the gunner's position without having to have forward momentum).
That is not to say that I don't want TDs included in the future-I do-I would just like to see the tanks that I think will get the most bang for their buck in the game before the TDs.