the .rmd is just text. But the output is cached separately, RStudio can load the full notebook, code and output. So it seems to me it's only a matter of how to integrate the .rmd with the output data so it can be displayed in interfaces other than RStudio.
Plus you get the option of rendering an HTML which IMO is no different than having a jupyter file.
Plus you get the option of rendering an HTML which IMO is no different than having a jupyter file.