Removing enrage timers would cripple gameplay.Also the only people who would benefit from it would be dps.It would mean they dont have to care about grinding gear.The damage tanks would have to endure would still remain the same and would encourage people to just play dps as they wouldnt have to grind out gear like tanks would.It would also make people not want to play healer as the longer the fight would go on the more stress they would end up in terms of keeping people alive and mana management.
Obvious top tier raiders would still want to get best dps possible but overall you'd kill tanking and healing in general gameplay.