Monstrosity: Players playing as monsters system.

[Genz]

Actually there is something like that already in the game, on both palace of the dead and heavens on high you can use certain pomanders to become certain monsters for a limited time.

Yes, that's totally the FFXIV spirit. We're talking about a system with hundred of playable monsters, no time limit, in the open areas, with their original abilities, a customisation subsystem ; but indeed it's already in FFXIV : a gimmick item in 2 dungeons for 1 minute of cosplay with 1 ability.