How about bringing back the old set bonuses:-

(Old 2 piece set bonus) Increases shield chance by an additional 5% during Dark Ward/Kinetic Ward.

(Old 4 piece Set Bonus) Increases Elemental, Internal, Kinetic and Energy damage reduction by 2%.

I think bringing back the old self healing tank game play would be very popular, Maybe something like this:-

While Dark Ward/Kinetic Ward is active you are healed by X% of your maxium health every second, additional when you gain a charge of Dark Bulwark/Kinetic Bulwark the heal increases by X% per charge.

Also maybe make tanking relics more useful for example, reducing the cooldown timer of certain defensive abilities (eg. Deflection, Force Shrould/Reslience).