the best medic rule Ive seen (and this should be standardized) is the one they use at trev's hill437
everyone is given a carabeaner latch with a piece of rope tied to it. the rope has 5 knots in it, each knot is a life. When you get hit, you have a 5 minute bleed out period in which a medic can get to you and untie one of the knots. If a medic doesnt come in time you walk back to your spawn point and take out one knot.
when your under fire trying to untie a knot it adds alot more challenge to the game. It makes the medic role fun as well. Sounds easy, but then take into account most of us probably wear gloves, and undoing knots with gloves isnt as easy.