A worthwhile question.
The real issue with crewability is the fact that you can choose a target and shoot, vs. watching the AI struggle at times.
It's not really about "fully modeled systems" to me, either. The simple M113 is a perfect example of getting functionality that imerses play, but isn't a whiz-bang system in all detail. (Granted, the track is pretty damn simple, but you see what I mean...)
My greatest interest usually lies in US/NATO vs. Warsaw Pact forces in theoretical WW3 scenarios. Some more modern ones are awesome too. But for any of those, what I want most is for both sides to be able to have a crewable MBT, IVF/APC and a functional (not necessarily crewable) CS/CSS selection of ENG, Arty, recovery, and logistics. The later can be abstracted, too. i.e. I don't need country accurate fuelers or ammo trucks, I'll settle for placeholders.
The weak link at this time is the USSR IFV. If we get a BMP, we "even up" the crewable platforms for each side. I'd also run the Marder as a close second, with the availabilty of DE equipment too.