I have always liked the idea for returning characters to be given a Fatality they are mostly known for or one of their orignial Fatalities. So for example in the next fighting version of MK we get everyone would have their 2 Fatalities and any character that was in a previous installment of MK should get a third (if there are any newer fighters in next game). Their trademark Fatality should be one they are most remembered as having or their first one they had. We saw some of these get revamped in MK(9). But here are some examples: (I gave descriptions of them)

Johnny Cage -- Uppercut Decapitation
Kano -- Heart Rip
Raiden -- Head Explosion
Liu Kang -- Dragon Tail Uppercut
Scorpion -- Toasty
Sub-Zero -- Spine Rip
Sonya -- Fire Kiss of Death
Shang Tsung -- Soul Steal
Ermac -- Telekenetic Slam
Reptile -- Head Snack
Kung Lao -- Cutting Opponent In Half
Jax -- Head crush
Kitana -- Kiss of Death where they swell up like a balloon
Mileena -- Swallows opponent and spits out bones
Baraka -- Impaler
Jade -- Staff impale
Smoke -- Smokescreen
Noob Saibot -- Spirit Swirl
Kintaro -- Torso punch
Sindel -- Scream off skin
Cyrax -- Helicopter head spin dicer
Sektor -- Compactor
Nightwolf -- Spotlight
Sheeva -- Skin rip
Kabal -- Remove mask and scream at opponent
Rain -- Lightning strike explode

If any of the above were in the next game along with newer fighters they should all get two Fatalities but the ones above would get one more. I just gave the MK1 - UMK3 fighters as examples.