IMO, the time and effort to mount, dismount, set up, fire, tear down, load up, move to a new position, ... repeat... would be far too much work and time consuming for a towed anything. It is better off, imo, to have said abilities mounted on a chassis that is already.
Having the SdKfz 251/22 w the Pak 40 (or KwK40), M3 w the M1a1 gun, the Priest, etc, makes a whole lot more sense for adding to the game. The chassis are already developed and each of the above mentioned would add a new dimension to the game as far as gv vs gv.
The triple 20mm SdKfz 251/21 makes for some fun. Hopefully, that would change the ENY of the Wirby and let the Ostwind and the 251/21 take some of the AA glory.