I have criticisms about the game and SE, but the hostility in this thread to even brainstorm how it could work suggests that nobody wants to give it a serious consideration, and it's been proposed by the
same people a few times. FFXIV is FFXIV, it's not going to grow by copying WoW, and
WoW, makes a lot more QA mistakes than SE does by miles.
Imagine for a moment a M+ feature for FFXIV that results in another Ungarmax. That's the kind of engineering mistake in FFXIV that can come from not testing things sufficiently. Let's say theoretically that any dungeon can become M+ by clearing it on minimum ilevel. Then it's discovered that you could clear level +20 by removing all your gear so the game naively sets the difficulty based on the entry gear stats being zero.
The way people in this game quickly attribute inaction from SE as "not a bug" is why I feel SE doesn't take risks.