I think this would be more something we would see out of ToD. I would think it would be implemented into the game to work with fighters who are at high altitude on patrol or aiding bombers to their targets. From what I hear, HTC is trying to make ToD VERY realistic, so I would guess there would be your occasional oxygen failure meaning you would have to dive. Once you're below 5,000 feet and at a resonable speed, pop open that canopy and get some fresh air.
It would also be something I could see the TBM's using in Midway scenarios. Or A6M's and D3A's in Pearl Harbor Scenarios. You didn't go the whole way with a canopy shut, the darn bombers were so slow you could afford to keep the canopy open on that A6M.