I would love to have an appropriate/accurate Stug III for early war gaming, but I doubt that will ever happen, from any model-making company.
Stug III A = 36 built. Saw service for the first time in France 1940.
Stug III B = 300 built. The tracks are wider, the drive sprocket and idler wheel are different, and the return rollers were repositioned. MAYBE a complete track replacement kit could be offered up to turn an A into a B. But that would mean first their needs to be a Stug III A offered up. And with only 36 built (and many people far more interested in mid and late-war models) I don't see an Ausf A ever being offered up. But they could do an Ausf B kit.
Stug III C = 50 built. Superstructure changes. Which means that the Ausf B kit would not work for the C. MAYBE they could offer a new upper hull replacement kit for the Ausf B kit. But there must first be an Ausf B kit.
Stug III D = 150 built. Externally identical to the Ausf C. So Whatever replacement superstructure kit that was offered up for the Ausf C to turn an Ausf B kit to the next version, would also work on the Ausf D. Or ... they could offer up a new kit that covered the 200 Ausf C/D versions.
Stug III E = 284 built. More superstructure changes. A replacement superstructure kit could be offered up to turn an Ausf B kit into an E, or the same replacement kit could turn an Ausf C/D into an E. But first we would need either an Ausf B or an Ausf C/D kit.
Stug III F = 366 built + Stug III F8 = 250 built. Superstructure changes, and the addition of two different long-barreled guns. There are probably too many parts that would be different to allow for an upgrade kit to one of the earlier kits to turn it into an F or F8. This would probably need to be a separate kit.
Which leads us to the offered kit of the Stug III G. 7,810 of these were built, and another 1,299 of the StuH 42. Which represents 86% of all Stug IIIs built during the war.
Again, if they offered up a kit of ANY of the Ausf A through Ausf E models, I would love it. But unfortunately, I don't see how a single kit could be used to produce all five of those versions. And once you produce a kit to only cover one (or two in the case of the C/D) very few were produced, and I suspect that makes their usefulness as a model kit very limited. And given the numbers built, of all the earlier versions a kit could be made for, the F/F8 is the most likely, and that doesn't help at all for early war accuracy.