I thought about this a lot back when I was playing live when they released shrouds.
Shrouding was supposed to be the solution to this , BUT was poorly implemented.
Shrouding abilities where ok but the primary one healing where severely gimped. The shroud at time where a combination of a lot of mix of classes with some being a lot of fun to play. Having to exp in shroud tree to unlock higher shrouds was genius.
Shrouding would be and Ideal solution for Planes of Power and down expansions. I had personally tested all shrouds in POP expansion.
shroud tanks could tank in pop tier 1 zones , you still needed healer to keep them up. <player tanks where better Obviously but they where not always available>
DPS shroud did decently in POP.
Healing shrouds failed miserably in POP the healing skill given to healing shroud where very limited.
I always felt shroud should have had their own level appropriate gear that would drop from common mob to named with quality going average to good respectively. This would have motivated higher level player shrouding down to get aa xp also hunt gear for his /her favorit shroud.
So many wonderfull possibilities with shrouds oh well