First off, I think dual spec will be added. Secondly, I think that most of the population who wants to play SoD mostly wants dual spec too because the game is being made for people for whom their character is THE reason to play, far above any other.
Having said that I hope, although don’t expect, that some restrictions will be put in on where to change specs (like a rested area).
To explain:
I used to have an impartial view of dual spec. People kept asking for it in tbcc and I’d just shrug think “Doesn’t matter. I can do world content and do most pvp (while just swapping for arenas 1 time a week), and raid with the same healing spec just fine”. So I’d move on.
Then came Wrath and at first things seemed fine. No different than before even with dual spec. However, then began the bad part. It was no longer what was fun. it was only and ever about what was best for the raid group regardless of fun. Both specs WERE for the raid group. Anything else, like a PVP spec, you needed to pay to respec anyway. Being expected to heal and swap to DPS at any point while competing as a DPS (parse) and while only ever getting just the DPS gear dregs was not fun. That led to raid night with a long-time guild going from a fun time to being something to dread. 99% of the fun was gone. It’s on the list of 10 reasons for why I quit Wrath.
This happens to people all the time.
So yes, any guild even trying to min-max (which is 90% of them) will expect this and it’s not about what’s fun for you it’s only about what’s best for the team. That’s why I’ve been trying to research what is the best class for SoD to where I won’t be forced to do that again even when dual spec gets put in (expected). Any second spec I’d want for PVP, not to accommodate the raid.