I don't see much of a point in adding specializations to something that is already pretty much a specialization.
Specs are usually used as a way to diversify whatever class was chosen in the beginning by adding different playstyles to it. Most games also allow to switch between spec to further that diversification.
This process is entirely unnecessary in this game, as you can freely switch between any jobs (or specs), regardless of what was chosen in the beginning. Any further specialization would be merely for flavour, and at that point, wouldn't it be more 'flavourful' to make a completely new job instead of something that merely bounces off of a job that already exists?

I see it this way: Rather then picking a class in the beginning and later on a spec, you skip the class and go right to choosing your spec.
Or: Every character basically shares the same, unseen, base class, with currently 26 specs to choose and freely switch between.
I know we technically do have classes but since they directly evolve into their jobs without a significant change in playstyle they are not really worth mentioning. The only class that does split into 2 different Jobs or 'specs' would be arcanist, and I'm pretty sure the devs are on record saying they don't really like that and would sooner split the completely then do it again.

Tl;dr: Jobs already are pretty much specs and adding specs to specs is unnecessary and convoluted, imo. (I hope people understand what I'm trying to say, I can't seem to english today :/ )