My thoughts:
1) Sure, eyesight was very important to RL WW2 pilots, but many (most?) of us are much older than any of them were at the time. Furthermore, most(all?) of our monitors don't have even remotely the same resolution as the vision of a young, healthy pilot. And our planes don't reflect the sun nearly as brightly as real ones. I can see an airliner flying overhead at 20k+ much better than I can make out a 6k+ dot in AH. All that adds up to this: Half or more of my deaths would to people I never saw not because I wasn't looking, but because they were smaller and more innocuous than a mote of dust on the monitor until it was too late to react at all.
There are many challenges I enjoy in this game, but testing my eyesight is not among them.
2) Assuming they'd still show up as red on the map, this would mean a huge increase in the value/tactical effectiveness of porking dar, because it would become the only reliable means of detecting enemies more than 2k out or so. IMHO dar is already too easy to pork and too frequently porked and this would only encourage it, but OTOH making it harder to pork would then give a huge advantage to defenders over what they have now.
3) Because of the above and the absence of ground controllers, clear and thorough communication of tactical info between all the members of a side would become much, much more important. I'm not sure our current radio capabilities could handle that much extra traffic, and it would be much tougher for newer players to learn and much more annoying for the veteran players having to hear the new players learning.
4) Couldn't the same thing be accomplished by having enemy icons at a certain range just be red range numbers, then as you got closer, 2 or 3k maybe, they would say "Ftr" or "Bmr" or "Hvy" (for 4-engine bombers), and only tell the plane type when you were up close - say, inside 1000 yards? That would satisfy the stated purpose - preventing players from having unrealistic knowledge of what they're facing 6k away - but wouldn't make as drastic changes to game balance as those outlined above.