Yeah, I think subclasses ideology is better.
First you pick your subclass, then your spec.
Lets take hunter for example.
Subclass #1: MM, Shadow Hunter (Old surv esq)
Subclass #2: BM, Surv, Tinker
It could work for a few other specs, however. It will not happen. It worked for other MMo's because they were integrated at the start. You didnt have set classes like WoW does, you had mix and match of classes. Each spell for intechangeable with different class/subclasses.
Like a warr/necromancer, would have the same spellpool available as lets say a mage/necromancer. That just isnt the case in WoW and I dont see it ever being integrated into the game.