AsciiDoc and RST/Sphinx are definitely more powerful for structured documentation with cross-references, includes, and admonitions.
For now Ferrite is focused on Markdown since that's the most common format for notes and quick docs. But the architecture could support other formats — the parser layer is modular.
If there's demand, AsciiDoc would be the easier addition (cleaner syntax than RST). Would be curious how many folks would use it as their primary format vs. Markdown.