It has been suggested a few times in multiple topics on official forum, in multiple forms, so i thought i will gather everything here in one topic.
I will describe these options from the easiest to the hardest to implement. If developers decide to add it, they can do it in that order, or everything at once if they have enough manpower.
Everything suggested here should be server side, otherwise it would make no sense.
1. I would call this "trait toggle". Some jobs at specific level unlock traits which upgrade specific action and change animation. New animation is not always better, and some people would want to go back. My suggestion is to add an option to disable specific traits which will revert animation (and obviously sound effect), while keeping the battle effect (upgraded damage etc).
For example WHM at 72 lvl has Stone IV replaced by Glare. Some people might still want to throw stones at the enemy. Or MCH at 64 lvl becomes master acrobat, some people may prefer staying on the ground. This option would let revert the changes.
I hope you understand the idea.
2. Full actions glamour system. It would let us not only glamour replaced actions by traits with their previous versions, but also use removed counterparts. Especially tanks have suffered after 5.0 rework.
For example DRK could use old Power Slash combo. Or glamour The Blackest Night with Stoneskin. Or glamour Rampart for PLD with actual old Rampart, etc. They could limit it to only removed counterparts, or analyze available animations to give us more choice. Or remove whole limits, beside obvious things like glamouring AoE moves on single target attacks.
3. This is expansion of 2nd point. If there are multiple animations available for one action, they could allow us to use random animation. We could choose which animations we would like for specific action, and one of the animations would play randomly when we use said action.
I know this shouldn't be their top priority, but in my opinion this is really brilliant idea (as i said it was suggested a few times, i'm only summarizing what has been said), and very unique. Also don't forget that animations and sound effects are very important part of how job feels like. That way everyone will be able to customize their experience.
They are able to do it, at the moment SMN has very simple glamour system for carbuncles. Now they have to expand it for all jobs and actions.
If you like the idea, or specific parts of the idea, don't hesitate to send them in game suggestion via support desk menu. If we won't show them that there is demand for this, they won't add it.