The truth here is that classes dont feel customizable because they arent because they cant and never will be. There will always be an optimal way to play a job (or pick an augment) and thats becoming the meta with every alternative being ignored and therefor a waste of dev-time - or, worse, being used by people who dont know any better and are then scolded or kicked for not playing the class the "right way".

Customisation in this game happens within your character, not within your job - by which I mean: You only have one way to play BLM, but three ways to play a caster.

Personally I think this is an idea thats bound to fail, wasting a lot of time on balancing when everyone is using the "best" augment anways once its been figured out what that is - just look at secondary stats: People dont pick and choose them based on wether they like crit or speed more, they're choosing them based on the BiS-lists people have figured out.
Considering that the team would also have to balance with every possible augment and augment-combination within a group in mind, I just dont think this has a real place in an MMO... or at least not within this one. Customisation works great in singleplayergames, but here? You'll have one build that everyones gonna use and the rest just going to waste.
I'd also rather get some actual stuff - even if its just adjustments to skills I already have - than getting 5 "skills" that I can only use one off.