What about other services for building websites like Wix?
First, be careful you can export your content safely and easily before you commit to a website service.
Now for being able to use a workflow like with the conceptual goodpress for WordPress you need
the service to provide an API for publishing new posts and managing media (listing, deleting, uploading);
to know what format the R Markdown output should have.
Then you’d need to write a script/package around that, using HTTP packages, rmarkdown, Pandoc, etc.
OR you could figure out what R Markdown output format to use and copy-paste to the post editor, and upload media by hand + tweak references to media path in the output.