I played a game with something like this I think. Maybe Diablo 3? I might be wrong, it's been a while since I've played whatever game it was.

Something like what you describe might be kind of fun depending on how it was implemented, though as multiple people have mentioned losing a character due to lag would be horrible. Just imagining being on a permadeath character and suddenly noticing that no one besides me is casting or moving gives me chills lol.

I agree that the chances of seeing this added to ffxiv are slim, but it's a cool idea!