IDK if people would hate me for suggesting this because it'd cause tanks to be going for gear they might not usually go for due to new builds opening up but I'ma still suggest it for the sake of build variety.
Right now for tanking into endgame (raids) the choices are Defensive Stance, Righteous Fury, or bear for threat generating stances. And temporarily you can spec into a lot of threat via metamorphosis but it's a temp ability. The current route for spell tank builds is to go Righteous Fury, get strength tank gear and be heavily mana inefficient. There are plate int defense hybrids but only in dungeons not raids.
A few REs I'd like to see implemented to boost viability for builds that are essentially teased but not very valid. All of these RE suggestions probably Epic+. Not going to think of catchy names myself nor of balanced numbers just of what sounds clean to me atm.
Metamorphosis RE- Metamorphosis is now a permanent stance, with increased threat generation, decreased damage, and a portion of intellect is gained as defense rating. Demon charge now has the same cooldown of warrior charge and same stun duration. Increases chance to block fierce blows.
Boomkin RE- Boomkin threat generation is severely increased, damage is decreased and a portion of intellect is gained as dodge rating. Stamina is increased by 20% (to be in line with Bears as Moonkin also cannot block or parry)
Weaponsmaster RE- When in Righteous Fury/Defensive Stance and wielding a single 2h or dual wielding 1h each hit has a chance to increase your chance to dodge and parry for 8 seconds with it stacking up to 6 times (double stacks per auto for single 2h), at full stacks you empower your next auto to apply to all enemies in a 8 yard radius causing heavy threat and decreasing their damage done to you by a small percentage for 4 seconds, removing all stacks.
Monk Combo RE - When in Righteous Fury/Defensive Stance and wielding a single 2h or dual wielding 1h Your armor contribution from leather items is increased by 80%. Your successful different attack abilities give you increased dodge up to 5 stacks, drops if you use the same attack ability twice in a row.