This is very interesting (I presume you've read other authors' comments on the accuracy of German 'on strength' reports, upon which 'Panzertruppen' as based).
I share your interest in early war armour. I think the issue is simply cost versus reward. The 'Blitzkrieg' period simply doesn't attract the same level of interest as NW Europe, the Eastern Front and the Desert War. That shouldn't be the case - arguably it's just as interesting from a technical perspective, and more interesting from an operational/strategic perspective. I think it probably just comes down to the enduring attraction of the late war AFVs (particularly German types). As a result, apart from a few one-offs (and vehicles that served into the latter part of the war, such as armoured cars), the early war period was generally neglected by kit manufacturers until relatively recently. A vehicle like the Panzer IV Ausf C would, if done properly, require a lot of different components to a later Panzer IV. That's a significant investment, when the aim would be to have as many common components as possible. I'd guess that most wargamers who wanted to game that period would be quite happy with an Ausf D (even if it was less common) - or even an Ausf E - as all they're really going to want is a Panzer IV with a short 75mm that basically looks the part.
Hopefully, as Rubicon expands, they will have the resources to focus on this important period, and do it justice with a balanced range of French, British and German subjects. Rubicon's style is well-suited to these early vehicles, as most of them had narrow tracks which are easily produced in one piece - there will be very little loss of detail. The subjects I'd love to see would include:
- Pzkw 38t
- Pzkw II
- SdKfz 232 8 rad armoured car
- Somua S35
- Panhard 178 armoured car
- A13 Cruiser
- MKIV Light Tank