With Tier 1-3 the sets were designed for the main spec of each class: Warriors sets for tanking, Paladins for healing, etc...
I feel they did this perfectly and should bring it back. Where the sets are only designed for the main spec / role of that class.
Now I hear it.. What about the BOOMIES / RETADINS?!?!! THAT ISNT FAIR..
look at how itemization was back in classic. Main specs had the tier set to make them stronger (Their own little Nitch) then offspec had the random gear that dropped off Dungeon/raid bosses. I feel this made the items dropping off bosses be more unique instead of the tier sets transferring its bonuses depending on what spec you are.
This Focus could even go farther into the fact that each tier set is designed to strengthen that classes healing / tanking / dps but make it more focused on what the main raid requires... a little more customization for each raid. Fire res increase in the set bonus etc.. increase dmg to UD... increase stun resist (bosses that stun).. just some random things that make the set unique and powerful to that raid that it drops from and then also over all.