We will not be balancing around the existence of dual-spec. The example I used was a case we already have – multiple tank fights, then single tank fights, then multiple tank fights. We didn’t design that around dual-spec. We assumed you’d probably have an OT who tried to do dps on Saph. Dual-spec gives them a way to do better dps.
This is one of the reasons though that we think it’s important to keep pure dps slightly elevated.
Mostly, though, dual-spec is a convenience factor. You can already run back to town and respec in the middle of a raid, and plenty of people did that already (and hated it).