I'm looking for either a blue post or GC tweet I saw recently where they hinted at entertaining this idea but in no way, shape or form promised us triple spec. Annoys me I can't find that post...
Anyhow, given how the talent system now works, we can now tweak talent layouts on a specific spec to fine tune it for either pve or pvp. Thus, the old method of using dual spec for separate pve and pvp builds of the same "spec" don't apply anymore.
As for me, being a shaman main, I would welcome it. I've played elemental and resto mostly since BC, but I've always said I would play enhance if I didn't have to monkey with redoing keybinds and whatnot every time I wanted to swap it in for one of my other specs. Pure laziness, yes, or convenience if you will. Nothing stopping me from spending the gold to change a spec. That didnt' stop me from spending 10k gold on acquiring dual spec for every character I had available for it when it came out, so I'm not a total cheapskate...just mostly a cheapskate. :P I've always maintained that I play a class, not a spec, but given how you're shoehorned into 1 or 2 specs of your class, it is more about the spec you are, not the class.
One thing I would not like about a triple spec: Yet ANOTHER set of gear to deal with. I'm just barely getting my main (ele) set caught up; I just started playing MoP again 2 months after it was out. Moreso, my bag space...wait, I wouldn't have any, lol.