I would get MoP s15 back with some tweaks. Removing symbiosys, putting clone and fear on same dr, fear breaking a lot quicker from dmg, remove poison stun from rogues, removing pom, making RoF cc go off instantly instead of delay, make monk portal instant and not a cast.
Would also nerf mage dmg by a bit. Might have forgot about some ability tweaks but those are the main ones imo. Game would be fun and good.
Something thats up for debate is blanket csing wether it should stay in the game or not.