Unless my memory is faulty (it is, but I mean on this fact in particular) pronouns are called by linguists a 'closed class,' which means that, unlike with nouns and verbs, you can't add new members and you can't take them away. Well, as my post about THEM shows, the members of the pronoun class can change eventually.
Now, this is actually controversial these days --I'm surprised how often I find myself thinking of grammar controversies. Who knew?-- in that we feel a lack of a third person pronoun that doesn't specify gender. That is, some people feel the lack; smart people recognize that THEY serves perfectly. End of discussion.
I thought I said it was controversial. Well, my mind is made up, but other people argue about it.
Back to the new pronouns I'd like to introduce. About ten years ago, a fellow linguistics student (in whose band I happened to play some drums) and I , having learned of the existence in some languages of different kinds of WE, decided we'd like to have some different first-person plural pronouns to choose from as well, to clear away some potential ambiguities. Jar-Jar fever had the land in its rubbery grip in those days, so of course one new WE was WESA, which would mean 'you and me and also everyone else in this conversation,' and to contrast with that, we proposed WENIS, to mean 'me and someone else, but not you.'
So now we could say 'Wenis are going for pizza,' and the Hooper Humperdinks of the world would know right away that we meant Not Them. But we never said it.
I guess we'd still want a WE to mean 'you and me but not anybody else' so the original WE can be left to cover that.
I wish I had more pronouns to propose, but it's not like there's a lot of room in the class. It's closed. Instead --even though it's not at all necessary-- I'll just destroy the objection to using THEY with a singular referent: no one has the slightest difficulty understanding that YOU can have both singular and plural referents, and that it agrees with plural verbs even when its referent is singular.
And citing tradition by saying 'we've always done it this way' or 'this is its original meaning' and therefore it must always be done that way, is a logical fallacy. I mean, it's not like we still say hem for them.
For a good read about a different closed class changing, here's an article from Language Log, by an actual language professional.