hi all, thanks for the interest/comments; I decided to write-up a page that details this on the docs.
http://inedo.com/support/documentation/proget/feeds/other-types
I'm hoping we can use this public thread to maintain the discussion on technical detail; otherwise it'll get stuck in my email, or somewhere else, and we can get everyone to chime in this way.
That said, @M-W if you've got any insight into how R/CRAN works please do share :)