There's some very interesting stuff in this thread!
I think the problem we have though is that the model of the P-51D that ED made was not seen in Europe and so, consequently, it makes it difficult to get a suitable opponent to this version of the aircraft... the Ki-84, J2M3 Raiden, Ki-61 Tony or Ki-100 would be the most even counter part, but the trouble with these aircraft is that they lack the popularity factor that the ETO aircraft have...
I think, in years to come, we will see all kinds of WWII aircraft but I think it will be a while before we start seeing some of the rarer, lesser known aircraft types in this sim. It appears, to me at least, we will be limited to the normal "Top 10" of WWII fighter aircraft... Mustang, Spitfire, 109, 190, P-47 etc... for a while atleast, as these aircraft will certainly sell.
Either way, if it was built between 1914 and 1955, I'll be buying it ;)