I suspect that my proposed "everyone is they" standard might lead eventually to a new suffix for when some kind of plurality specifically needs to be distinguished from something else. We already have the example of "you" growing suffixes for kinds of plurality (you both, you all, y'all, and the terrible 'youse guys'), so it wouldn't be much of a leap for English to do the same here (they both, they all). Those word pairs have already been used, so there's some measure of consistency to it. It's not awful, at any rate.