This is excellent!
You know what it lacks to really be perfect?
Stat blocks for typical NPCs (Templars, Halfling raiders....The Dragon) and maybe some spot rules for desert survival.

I doubt I'd stat out npc's as they should be rather easy for a GM to put together and have a bunch of basic stuff in the minisix book that can be referenced and tweaked.

Desert survival though is something to think about since it is a harsh harsh world.  Probably want something simple but still dangerous.

Added new perk for Head Adaption and rules for Heat Exhaustion.  let me know if you think they are to harsh.  Trying to keep the rules not to complex but still feel like original dark sun.

Wouldn't it be easier if Heat was just a normal damage roll?
Like:
Every 4 hours in the desert roll 1d base damage
+1d for no water in the last 4 hours
+1d for no water in the last day
+1d for extreme heat
+1d for no food in last day
armor adds to damage instead of adding to Soak.
You can use Stamina skill as a base for your Soak value instead of base Might.

Stun damage from heat is not healed until you can get rest in the shades
If you accumulate more Stuns than you have Might dice you become unconscious for 1d6 hours.

Characters in cities or other settlements do not need to roll because they can usually get enough shade/rest/water to keep going without problems unless the GM states otherwise.

Too convoluted?

Looks interesting.  I may simplify it even more just to make things not TOO complex.  How about adding a Fatigue system sort of like Savage World.

Fatigue: Every character has 4 levels of fatigue.  Every point of Fatigue reduces your dice pool by 1D.  After 4 levels of Fatigue characters falls unconscious and has chance of death if not saved.

very 4 hours in the desert without water roll Stamina TN 12 or take 1 Fatigue damage.

Modifiers:
Water: If character cannot drink at least half gallon they suffer -2 to Stamina roll.  If they get no water it is -4 penalty.  This is in addition to Fatigue effects.
Resting: +1 to Stamina roll if character stops any physical activity
Shade: +1 to Stamina roll if character can stay under significant shade.

looking for 2 players for a play by post game.  send me PM.

Added Channelling rules for casters so for those harder to cast spells they can do it over time but if they are hit the spell is interrupted.

Changed defiling to be +2D on magic roll.

Added new perk Armor Optimization which reduces the initiative penalty by -1 for armor wearing.

Dragon of Tyr

Scale +4D

Might: 5D
Agility: 3D
Wit: 6D
Charm: 3D

Skills:
Brawling: 7D
Breath Attack: 7D
Magic: 9D
Psion: 9D

Attacks:
Bite (Normal Scale, 9D damage)
Tail Bash (Normal Scale, 9D damage)
Breath Weapon 3x Day (Super Heated Sand - 15D damage range 50 ft Cone)

Perks: Scales (+10 armor), Fly 90 ft/round, Drain Life, Resist Magic/Psion +8
Static: Dodge 9, Block 21, Soak 15 (25)

Magic: Knows all Wizard/Psion powers