It seems to me that Blizzard is not so much making hybrids that can change roles easily and be good at everything all at once... I think they are giving players more choice when it comes to speccing their character a certain way, but once you've chosen your spec then you're generally as specialised as the next guy.

I think the real benefit that a lot of these "off specs" will bring are the extra benefits they give to others. Moonkins will give benefits to other casters, ferals will give benefits to other melee, shadow priests will benefit mana users, shamans will have totems to benefit others depending on their talents.

I see the struggle for a good raid make-up will be having enough off-specs to benefit the "purer" classes/specs while not going overboard and diluting your healing and dps. It feels like there will be a lot more options, and a lot more choices to make things interesting.

Moonkin benefit melee now too, just for the record, with Improved Faerie Fire, something that will be more useful towards the start of the new 25 man raids, due to the new hit rating system. Improved Faerie Fire provides a flat 3% hit to all melee and ranged, as well as the moonkin aura giving your 4 best fire mages an extra 5% crit. Will be very nice indeed, especially when crit and hit levels are much decreased from their level now.

This does rather raise a question as to the wisdom of having talent trees in a class-based game, though. If a Druid is just a Priest that you can turn into a Mage or a Rogue by spending 50g - that seems a little pointless.

I think if Blizzard achieves their goal (which might be a big "if"), there will be no such thing as a "mainstream spec." Hybrid classes will be judged not on their ability to perform a single role, but rather on their ability to change roles as required by the situation.

I'm guessing that we can expect 25-man content that requires a total of 35 roles to be filled at various points in the content. Hybrids will need to be able to switch between tanking, healing and DPS as the raid moves from encounter to encounter (or even from phase 1 to phase 2 of an encounter).