Thinking your existence is determined by the grammatical structure of language is a self defined prison of ones own making.
Ok cool, they get to exist. And they speak Spanish. What word do they use to refer to themselves?
Oh, no, how did we get back here...?
There are new terms added to the lexicon every day for each persons individual experience. They can refer to themselves however they wish. Yet, it is not reasonable to think that unlimited possibilities can be assumed to be known and forced into the grammatical structure of language. It begins to drift into much broader domain of identify expression of simply how I wish to be known. Not every concept of how I want the world to see me could be expressed in a single grammatical construct of language and it is a futile effort to do so.
Spanish-speaking non-binary people are hopefully not so stupid as to conflate a lack of appetite to rewrite the entirety of Spanish grammar with a refusal to acknowledge someone's existence.
You will actually find that the vast majority of Spanish grammar is untouched by this change. The only change, actually, is that it will now be possible to acknowledge the existence of nonbinary people. Or do you think that binary gendered pronouns already do that job?
Except progressives are pushing LatinX as the default term that all Latinos fall under.