This wish is based in ignorance of the way the systems existed in bomber aircraft, and ignorance of the design required to represent them in the game. In fighters it's a simple bottle, perhaps, but it goes far beyond that when you are talking about a life support system. The bottle itself is only part of the system. Of course the OP focused on that because it is the simplest way to think of a critical hit. However, there are several other ways to knock an aircraft down which he has ignored. Mostly, I think this wish is a waste of time because I believe Hitech has probably already taken considerable time in contemplation of exactly what a critical hit might be, and whether we are aware of it, or not, has already included them all in one form or another.
You sure love taking presumption to new heights (ptp). First you imagine motive. Next you imagine ignorance. Then you try to use that imagination to shore up a stronger emotional argument while trying to make it sound like a purely logical one. If you have a logical rebuttal, why do you apparently feel the need to go beyond that?

Where this wish is very thin is with bombers where the system is multiple bottles, some of which are already in the aircraft. Jump in a B17 and those yellow containers inside the aircraft are O2. Only a small portion of them are in the game, though. [What?! Heh.]Also, bomber aircraft have all got portable units and likely enough for all individuals plus extras too. They had to have them because unlike fighters the bomber crew sometimes must move around inside the plane to take care of various tasks. So, in reality this will not have any affect upon bombers if, as you now want, the entire system is reproduced.
" Mission 8. October 18, 1944 - Kassel Germany."
"Bombed aero-engine and parts factory; B-17 #009. The oxygen supply in the cockpit and the nose ran out over the target. For two hours Page, Lentz, Kellogg, and Vieth filled portable oxygen tanks and carried them through the bomb bay to the pilots in the cockpit and the navigator and bombardier in the nose. Finally had to let down over enemy territory because of lack of oxygen."
http://www.100thbg.com/mainpages/history/history3/brownsclowns2.htmHaving said that, let me correct you on the perspective of the OP since you're not very good at guessing. When it came to a suggestion of a possible oxygen system and hypoxia effect I always thought the bombers were more resilient .... for reasons even you haven't thought to include in your argument. Basically, unless we're talking about a crewman segregated from all the rest (tail gunner) if one is suffering the effects of hypoxia then it will become evident to another. On the flight deck, this would mean pilot and co-pilot would both both have to be suffering it (as in the above quoted instance). Fighter pilots, however, would not have that added measure of security. At extreme altitude (say 30k+), if the O2 system failed (in a less
explosive manner) the pilot would be prone to a rapid blackout with no warning then a very short time span before death. Even if the pilot survives the effects of hypoxia, regaining consciousness once below 10,000 is not guaranteed (but isn't merely discounted, either). Yes, the danger presented in losing your oxygen increases with altitude (isn't this established as an obvious by us both, by now?) but the likelihood of what I'm suggesting would be a small percentage of the damage algorithm anyhow. At this point I've seen you waver between this being an 'end of AH' issue to a completely irrelevant/waste of time one. I've seen a great deal of effort, on your part. If I 'didn't know better' I'd say you do somehow feel either threatened by the idea .... or you're the type that takes disagreement to a whole new personal level (not that it has to be 'either or' ... either).

Among fighters the most likely cause of an O2 explosion is a hit by explosive ammunition, which requires just a proximity hit to destroy the O2 bottle. Anything else will require a direct hit, which means you are more likely to have also gotten multiple hits. Anything like the explosive ammunition or multiple hits will already (currently) kill a fighter. Again, wasted development.
While you may argue probability, you cannot argue certainty. Perhaps the explosive hit was not
in the cockpit ... yet shrapnel made it into the cockpit and severed the hose. Perhaps it's not a case of several rounds entering the cockpit but one round, the rest of which stitched the fuselage ... or even missed.
So, in conclusion, all Hitech has to do is say "it's already in the game" and it is, because it obviously is. Now, you will say, "yes but we don't have an hypoxia effect," but you do. It's called a pilot wound. Now you might claim that with hypoxia you have the possibility of clearing your head. Nope, most victims died anyway and the reason is simple; they never knew it. The way most people today discover they are under the effects of hypoxia is communication, which in the war was non-existent because of radio silence. Those are the ones (some of them at least) that just flew off never to be seen again. End of story.
If pilot wound = hypoxia ... it would stop being a pilot wound (or never would have been one) under 10k. Kinda pokes a hole in and lets the air out of a " ... "it's already in the game" and it is, because it obviously is." statement. (Again - ptp)

Pilots on oxygen who experienced violent damage to their O2 system (without bottle explosion or personal injury, as slim a chance as you give for such) would certainly know when the O2 flow ceased and, depending on altitude and reaction time, may be able to descend to a safer altitude before hypoxia rendered them incapable. What you're describing would be more akin to system failure of a different kind (insufficient O2 flow either through mechanical malfunction or pilot error).