There are programs (LyX, TexMacs) that implement WYSIWYG for LaTeX, TexMacs is exceptionally good. I don’t know about the standards, though.
Another problem with LaTeX and most of the other document formats is that they are so bloated and depend on many other tasks that it is hardly possible to embed the tool into a larger document. That’s a bit of criticism for UNIX design philosophy, as well. And LaTeX code is especially hard to make portable.
There used to be a similar situation with PDFs, it was really hard to display a PDF embedded in application. Finally, Firefox pdf.js came in and solved that issue.
The only embedded and easy-to-implement standard that describes a ‘document’ is HTML, for now (with Javascript for scripting). Only that it’s not aware of page layout. If only there’s an extension standard that could make a HTML page into a document…