This problem is so easilly solved...
Keep everything as it is now. ONLY 1 CHANGE IS NEEDED!
Item budgets should not increase by %, but by a STATIC VALUE!
Example:
Tier 12 --> Tier 13, +400 strenght (or any other vary of stats)
Tier 13 --> Tier 14 +400 strenght (or any other vary of stats)
Result 1: After cataclysm the items would have had their stats increased by 1200
Result 2: After Pandaria the items would have had their stats increased by 2400
Result 3: After expansion X the items would have had their stats increased by 3600
INSTEAD OF THE 39k stats at the end of 95.
In other words: Make the item budget LINEAR NOT EXPONENTIAL
-Vaem/Varox/Astion w/e