IIRC, isnt there an EW version of the SdKfz 251 w/ a 20mm AA mounted on it?  That would be the best way to add another AA platform in to the EW/MW arenas.  No sense in making a whole new chassis if they dont have to.
HTC could introduce another 10+ gv's, or gv platforms rather if they'd just use existing chassis.  The SdKfz 251, M4 Sherman, and T34 all offer lots of options for easy expansions.