Concepts from other MMOs that would be utterly anathema to FFXIV

[Frosthaven]

So a couple of my own thoughts:

Gear corruption is a random possibility every time you loot gear that the gear will have dark void corruption on it, a stat that is tracked on your character that the higher it gets, the more messed up things happen to you, but in trade you also get extra power and damage.

WoW's gear corruption is waaaaaaay too rng to be what it is. It makes up a great portion of any individual's contribution but feels entirely unearned and random. I absolutely hate it as-is in the game and it messes up any feeling of earning/progression over time. Keep this to AARPGs, not MMOs.

When I consider how mechanically and culturally hard FFXIV leans into making sure everyone in your party is "vetted to be here,"

This is only true in some very specific end-game scenarios (such as Ultimate). FFXIV outside of those settings is one of the easier MMOs on the market by a fairly wide margin. Even the difficult stuff is typically hard-scripted, so it's just a matter of learning the dance and then dancing.

So how about you? Have you ever played another game that did something that made you think "Oh my god this would blow FFXIV's mind" and what was it?

Oh for sure! I'd love tab targeting and macro targeting from the older WoW expansions to be copy and pasted in. I would also love instanced housing like Wildstar had - for all its faults it really nailed housing down.