Quote Originally Posted by JoseB View Post
No. Singular "they" still is as "popular" as it has been, and there was no particular decline in use after 1850, very particularly in spoken language (which is the one that tends to mark the path of language evolution).
That's strange, I've heard several people complain about singular they as confusing, annoying, unnatural, and incorrect, compared to neutral male pronouns. In the wikipedia entry on singular they, it says that:
A majority of The American Heritage Dictionary of the English Language usage panel "of some 200 distinguished educators, writers, and public speakers"[32] "reject the use of they with singular antecedents" inasmuch as 82% of the panelists found the sentence "The typical student in the program takes about six years to complete their course work" to be unacceptable.
The article also mentions that “Current debate relates to not only grammar but also to wider questions of political correctness and equal rights, and in particular, the extent to which language influences thought.”, which matches my experiences. Besides, I'm pretty sure all the manuals advising against (or even forbidding) singular they is bound to have had an effect. I'd be happy to see some documentation if it's not true, and if the use of singular they 50 years ago was as great as 150-200 years ago, and if many people believed singular they was unacceptable before the manuals advising against it.
No, I thought we were talking about languages in general. The "extinction" thing was in response to your comment about "how would it feel if you saw your language going extinct" a few posts ago.
So we are talking about languages in general, and how and when they change, and for which reasons?
Languages are neither "allowed" nor "disallowed" to change, in my opinion. Languages change by themselves at their own pace. And changes depend on what might be called "linguistic inertia".

It is one thing to change (or extinguish) a language spoken by 2000 people (or spoken by 100 people, like the English spoken in the egalitarian commune of Twin Oaks in Virginia -- the people living there use gender-neutral "co", but then it is a community that chooses who comes in to live there in the basis of acceptance of the rules). It is a very different one to change a language spoken by 400 million people (or close to 2 billion globally, if we count 2nd-language speakers as well). In the latter case, change will happen, but will happen at the pace *set by the language itself*.
As I mentioned earlier, Iceland has made it a policy to invent new words, and though it doesn't completely prevent the presence of loanwords from other languages, a lot of new, Icelandic words have been implemented this way. Iceland does have a rather small population, but it's still more than a hundred times larger than the tribe you spoke of. I know Denmark and Norway also have language counsels to advise in matters of language, and I'd be very surprised if the other Nordic countries didn't have something similar.

Also, you've not yet explained how new words get implemented, if they can't get implemented by people suggesting a new word, which gets picked up by others. You use the words 'by itself', or variations thereof, a lot, but what does 'by itself' mean?
Nonetheless, both these situations do not alter significantly the underlying grammar and structure of a language. For that, you have to let the language evolve by itself. Pronoun gender (or its lack of it) is part of that aspect of language.
The implementation of gender neutral pronouns wouldn't change the structure of English. English words don't usually change when the 'he' in front of them gets replaced by a 'she' or an 'it', and therefore logically wouldn't change when replaced by a 'zie', or whatever word you prefer, either. It's just an extra word, used by some people when they feel that existing words don't suffice, it's not a fundamental change to the language.