The correct decision is a melding of model 3 and model 5. Every "pure" DPS spec needs to become a hybrid, but not by getting a tank or healer spec, but by being given a true fourth role.
The problem with the way this model was implemented in Burning Crusade is because the utility specs weren't really utility specs. They were DPS specs who brought utility while performing a DPS rotation. The poster child of this, the Shadow Priest, had no option to do DPS at all since the other two specs were both for healing. It was too specialized, as you had to have a Shadow Priest, not any of a handful of specs that brought utility.
To really make model 2 work you have to really commit to it. Dungeon finder needs to create groups of a healer, a tank, a utility spec, and 2 dps. They need their own forum, and the way they bring utility shouldn't be exactly the same as doing dps, except they do less of it. A true utility spec should have different gameplay and be making different decisions then a damage dealer.
Take all of those interrupts, crowd controls, offensive dispels, and non-damaging debuffs and put them on one spec. Give the arcane mage time warp, polymorph, etc... Make it so those players that choose Survival, or Affliction, or Assassination are those DPS party member who are always looking to interrupt, or the first to volunteer when something needs dispelled or cc'd. Then support that fourth role in your dungeon design.
It could be good for the game in a lot of ways. It would reward those former dps players who excel at those tasks extra tasks and want to shine at helping their party in a different way than tanking/healing. Plus they would probably have shorter queues than their pure damage dealing alternate specs.
It also clearly communicates that when you choose damage dealing, that's what you will be doing: dealing damage. Those players who only want to pew pew would only have to worry about not standing in the fire and not all that other stuff they thought they were going to get to avoid by picking dps. It could also help dismantle the "arms race" of every spec getting their own interrupt/cc/dispel/self-heal...etc...
It could also be damaging by increasing queues and making it a little bit harder to form a party. But there would no longer be anything called a "pure." And Players supposedly hate homogenization right? Adding a fourth role would be a big, bold step away from homogenization.