I think CoD should move away from regeneration health and move toward a bleed out method. If a person is shot they slowly begin to lose health, as their health drops, visions is blurred, and accuracy with a weapon drops as well. A single shot will stop bleeding over time, but no health is regained ever. Multiple shots will take longer to stop bleeding or will not stop at all. As your health decreases, make them able to sprint for shorter distances, take longer to reload weapons, longer to ads, blurry vision with the edges become black until they finally cannot see before they die from bleeding to death. No this is not hard core either, for this would be beyond hardcore where just a simple one shot kills no matter where your hit. No this is not last stand either, since it is not a perk.
I know many people will come here and go the game is not meant to be realistic... blah.. blah.. blah. And the only reason why is because they would fear such a system because they could no longer rush like fools get hit, duck behind cover wait for full health and continue on like nothing ever happened. It would make players have to be cautious and play tacticfully and not like adreanline monkeys rushing for kills all the time. a few near misses and slowly they begin to die, thus maybe loosing their streak becuase they did not take time to look around before moving.
The rushers and anti-campers will of course hate this because they will say it will make camping even more prevalent in the game becasue people will become to scared to even move. To the person with greater gun skill it would not be an issue since they would still hit their mark and kill them more times then being hit themselves, so not have to worry nearly as much about it. Only after repetitive hits during one life would the problem become bad enough for them.