I think you can use xaringan::inf_mr with any Rmd document with HTML output format, not just xaringan slide. Have you tried ?
html_notebook() format also have a preview mode which is really interesting: You work inline in the document by running chunks as you work, and each time you save the document, the HTML preview is updated. You can have both the source and the HTML result open in two windows. Have you tried that already ?