If you decide to sign up for Vrite, it provides a JSON output accessible through the API. You can then process it to any format you want using JS SDK and Transformers.

MDX doesn't make a lot of sense though as, with the supported features, it's basically the same as pure MD. That said, custom content blocks are in the pipeline and once that's added, MDX, MarkDoc and other formats will work really nicely with Vrite.

Try motif.land