I was thinking about the glamour system in FFXIV and lamenting the lack of storage in the glamour dresser and all the overflow glamour items sitting on my retainers. I started thinking about my favourite glamour systems and immediately the system in Guild Wars 2 came to mind.
For those that haven't played Guild Wars 2, when you get a new armor item, you can unlock the skin of that item to be used for glamouring other armor items. The skins that you have unlocked are just kept in a browsable list/database and you can apply them to other armor (of similar type - ex fending, casting, healing, etc) as many times as you want.
And thinking about FFXIV's glamour system, I think it can be tweaked to be a similar system. I was bored so I mocked up a prototype of what GW2's glamour system might look like in FFXIV.
Unlocking Glamours
Here goes! Once you get an item with a glamour you haven't unlocked yet, you could just right click on the item and in the context menu there could be an new "unlock glamour" option. They could add a line to the mouseover tooltip for each item to show whether or not you have unlocked it already. This would make it easier when rolling on loot in dungeons/raids to quickly see if you have that glamour skin unlocked already.
If it was an item that is tradable (ex. crafted gear), when you unlock the glamour it binds the item to you so that it is no longer tradable. This is so that people couldn't just craft one item and pass it around to all their friends to unlock it as well. When you click the "unlock glamour" it could give you a warning that the item will become untradable so that you have a chance to cancel it if you want. For untradable items (ex. raid or dungeon gear), you wouldn't need any kind of warning.
Browsing Glamour Collection
There would need to be a way to check which glamours you have and haven't unlocked, so there could be a glamour collection panel similar to the achievement panel or the challenge log panel. I know they're going to be changing the look of the achievement panel in Endwalker, but I couldn't find any high-resolution versions that were populated with achievements so I just went with the look of the current achievement panel.
This is what I came up with so that you could hopefully explore your glamours. There could be a count of the total number of glamours you've collected, buttons to filter complete and incomplete sets, categories down the left side, and maybe even a search button to make it easier to browse your collection. It could look and function very similar to the achievement panel.