The demo video at the bottom of the page shows that it can output to Markdown easily.
So, why did we create a Markdown data processor for CKEditor 5? (You can find a demo of it here: https://docs.ckeditor.com/ckeditor5/latest/features/markdown...) It was just to showcase that you can actually do that. But I'd never recommend it to anyone. HTML as a format is standardised and stable and there are even more tools to process it.
PS. There's the CommonMark standard, but it was created too late and its adoption is low.
PPS. We actually wrote an article called "A Standard for Rich-Text Data" – you can read it here: https://medium.com/content-uneditable/a-standard-for-rich-te...