The problem as I see it is that like WWI, the Spanish Civil war enthusiasts make up a very small percentage of the whole. There just isn't enough of them that would stay to make developing it worthwhile.
AH has the potential to do several such arena's. Including the Spanish Civil War, Korea, etc.
The problem is the amount of dev time required to produce the planes needed.
If the HTC crew can ever find a way to shortcut that process, then it would be a viable alternative. Also as hard as it is to find good data on WWII planes, it has to be tougher to find good data on those even older birds.