I have already started a similar thread in "General Discussion" to share it with other players to learn others opinion, and from what I saw the feedback was positive.
We have lost quite a lot of unique skills from multiple jobs due to need of unloading our hotbars for new skills:
Ninja's Dancing Edge, Mutilate, Jugulate, Shadewalker and Smoke Screen;
Dragoon's Phlebotomize, Ring of Thorns, Impulse Drive and Power Surge;
Monk's Touch of Death, Haymaker, One-Ilm Punch, Steel Peak and Howling Fist;
Dark Knight's Scourge, Delirium (HW attack), Darkside, Blood Price, Dark Passenger, Dark Arts, Soul Survivor;
Warrior's Mercy Stroke, Fracture, Brutal Swing, Unchained and Deliverance;
Paladin's Shield Swipe, Flash, Tempered Will, Sword Oath, Bulwark;
All 3 old Tanks enmity combos;
Bard's Wide Volley, Flaming Arrow and Misery's End;
Machinist's Rent Mind, Grenado Shot, Lead Shot, Heartbreak, Blank, Both Reloads, Rapid Fire, Cooldown;
White Mage's Aero III;
Scholar's Bane, Shadow Flare, Miasma II;
Astrologian's Stella and Time Dilation;
I am sure I didn't mention even half of skills we have lost. Each and every single animation of those removed skills and spells were meticulously created by professional 3D Designers.
Would be quite wastefull if we will only be able to see them on Youtube from now on.
From what I know all those animations are still in game.
So, it might be nice to see a system where we can customize visual appearance of our current skills with it's removed counterparts.
This can also be usefull to players who would prefer an animations of lower level simpler skill to higher level skills (like Stone II instead of Stone IV, Warrior's Steel Cyclone instead of Decimate or Machinist's not Heated main combo skill's)
This can be implementet in the same way we can change the size of Summoner's Bahamut via macro. Something like:
/skillglam "Aeolian Edge" "Dancing Edge" (/skillglam [Actual Skill Name] [Removed Skill Name])
And like with Bahamut's size this changes probably should be visible to player himself only.
New (old) animations can be unlocked to player's at levels they don't recieve any skills or traits to make their leveling more interesting and rewarding (right now, with max level cap raised up to 80 some jobs don't get anything new for 10 levels or so).
This system already exist in game in some form. Besides being able to change the size of Bahamut - Summoners can glamour their's Egi's with a use of a macro, making it so the next time you use your Summon skill you will have a Carbuncle instead of a usual Egi. Since all this skills already exist it's mostly about reusing already existing assets.
If developers desire to push this even forward later - we also can use for our skills customization some of old Heavensward PvP skills and also we had Logograms from Eureka. Also some folks asked a few times during FF XV collab event if we can Glamour our Gap closers (Tanks, Samurai and Red Mage) to that Noctis's Warp skill we were using during Garuda fight
Anyways such Glamour System should be a good way to save game's legacy and indugle player's nostalgia.
Also it would be cool to have one more innovative thing that FFXIV came up with before WoW. (There is no such system in Wow yet, right?)