Currently in 6.0, mods are ADDITIVE which means that players add mods to increase their stats, but this is seen as confusing for casual/new players, but critical for those players that want to maximize their playstyle/performance.
My suggestion is that you make all gear moddable, BUT, the mods are changed to be MODIFIERS/ADJUSTMENTS where you increase one stat by sacrificing others.
EXAMPLE:
Current Alacrity Augment 73, adds +95 Alacrity Rating, +126 Power, +126 Endurance
Suggested Alacrity Augment 73: +95 Alacrity Rating, -45 Power, -50 Endurance
In this way, mods are no longer a must-have and do not lock out the casual/new players since they are not needed and do not increase the gear. They do, however, allow advanced players to customize their playstyle/performance by adjusting their stats.
Mods should also by locked to the same iRating of the gear to prevent gaining advantage, i.e only mods of iRating 276 can be inserted into iRating 276 gear.
This will also give crafting professions new recipes.