Ah, I see. Thank you for the explanation, I think I got it now.
Basically - armoured platform for variable weapons.
Might I suggest taking an armoured car - like the personnel carrier - for now, with then-obsolete tanks modified for that role once they're, well, obsolete?
Basically, as I see it, the APC can mount an MG and transport infantry, too. The light cannon's a bit more difficult, but a tank could be used for that. And, lastly, the anti-air vehicle would suffice with splitter-proof armour (as it usually should not be used directly on the front lines, anyway) for now.
So, to sum up, we need three different classes of vehicles: Tanks, personnel carriers, and 'special vehicles' like anti-air ones or self-propelled artillery. Tank destroyers, possibly.
The personnel carriers will not be obsolete that fast - they cannot survive tanks, anyway, and don't need to be upgraded with them. So, tanks need to be upgraded fairly frequently. Old, obsolete tanks form the new special vehicles by refitting them.
Comparing your proposed vehicle with the APC, it's probably similar to compare the
Sdkfz 222 Aseaheru posted with the
Sdkfz 251 - similarly armed, similarly armoured and can be used with different weapons - like the standard MG, a mortar, a 75mm cannon or a small anti-aircraft one. (Not all at once, though.)
The Panzer is a very close fit to my initial idea.
I'll try to make it halftrack but thats no big deal if it proves to hard. But the flatbed on the back is perfect to just extend the armored cabin over and mount the guns ontop of to make it more useful for infantry battle.
Flatbed is fine for AA but in an infantry battle it's horrible.
Oh, it's no panzer, it's a Panzerspähwagen - basically armoured recon vehicle. There's a difference there
But yes, that's basically what I meant with my text above.