Are there any examples of neopronouns for non-binary or third gender people being fully incorporated into a language's grammar?

The case of hen in Swedish is the closest example I know of. hen does have a generic usage for people of unknown gender---so it does not fit your question exactly---but in most cases without explicit metalinguistic commentary, it's impossible to know whether a grammatical gender system arose due to social gender forces. We would not want to say Finland has no social gender simply because their language doesn't mark gender in its third person pronouns, so we would not want to claim the reverse even if we came across a language with multiple personal pronouns. This doesn't mean there are no examples of language users explicitly adopting a pronoun for non-binary gender reference.

In the last few decades, Swedish speakers have borrowed the Finnish hän as a gender-neutral third person singular pronoun. Finnish, a language neighboring Swedish, does not mark gender in its third person singular so its pronoun was seen as a good candidate for a new gender neutral pronoun. Adoption was resisted for a while, but in the last decade has seen widespread usage. It has been recognized by the Swedish Academy and is included in their glossary of the Swedish language, and the Swedish Language Council has commented on the proper inflections of the pronouns.