Spare athought for the allied modeller, your bemoaning the fact that only 4 of the major variants have been kittesd by no less than three manufacturerss, plus the others that were added and we the allied modellers are yet to see a medium or heavy AA gun except in expensive resin. We have a gun tractor for the US 90mm but no gun! In fact we are still waiting for basic infantry anti tank guns with two 70's kits (and fairly mediocre ones at that) of the venerable 6 pdr.
Be happy with the stunners that AFV, Tamiya nad DML have given you

I was thinking along the lines of the fact that AFV Club, by already making rubber tires and other molded parts that would go on the Pak 43 and Flak 41, wouldn't have a lot of extra difficulty in making the other guns as well. After all, the other guns were quite widespread in use as well.

Well not really. The Pak 43 shared no parts with earlier guns. Its trailer was the SdAnh 203 (I believe) and no other artillery piece used this. The 8.8cm Flak 41 used the SdAnh 202 trailers, which are the exact ones included in the DML 8.8cm Flak 36 and Flak 37 kits (that's where I snagged mine from for my build). DML actually is further along (using their Flak 37) in making a Flak 41 than anyone else. HTH