Hi bro, I'm into that quest too.
Regarding stage brutalities I have pretty much the same info as you.
(Though I could do the Dead Woods one by not connecting the stage interactions, just using them.)
However, I have found some cool things.
-Kotal Kahn's 6th is by using Blood Sacrifice. Have no idea how to unlock it yet....
-Kung Jin 6th brutality(Throw one) is not hidden, but I still can't find it. It must be by gambling.
The 7th might be the second version of the Shaolin variation, in which you can direct the Chakram up and down.
-Some brutalities have 2 different outcomes, which may indicate that those are "hidden", so to say. The ones I know of are:
Johnny Cage's Nut Punch (EX and normal give different outcomes)
Kung Lao's Hat Toss (directing up and down and Buzzsaw variation = 3 outcomes)
Goro's Shokan Grab (Dragon Fangs variation different than the other 2)
And, Shinnok can steal some brutalities by stealing moves with Impostor variation. I tested every char, and these are the ones who work.
I am still not sure if the requirements maintain or not. Some worked without, some worked only with.
Kung Jin (Steals EX Cartwheel Smash, didn't use 3 during the match and worked)
D'vorah (Steals Ovipositor Charge, must hold Fwd to work)
Mileena (Steals Ball Roll, must hold Dn, didn't connect 5 and worked)
Sub-zero (Steals Ice Ball, freeze and uppercut, works)
Ermac (Steals EX Force Lift, must do 5hit combo, used Fwd+2, 2, 4 and Force Lift to work)
Sonya (Steals Leg Grab, must do 5hit combo, used JI 2, Fwd+2, 2, 4 and Leg Grab in corner to work)
Also:
Goro (Steals Stomp, but couldn't test it yet. Need 2 controllers to make the loser defend on the final hit)
I'm really eager to find more too, lol
Btw, have you found Ferra/Torr's und Kano's 6th brutalities? I know it's by gambling, but still no luck here.