Nice. Amazing work. So buster should be covered then. Now (correct me if I am wrong) if we could adapt your scripts to create versioned Breaks: relationships with these packages, this would open the possibility to create backports for stretch-backports and jessie-backports- sloppy, taking advantage of the Debian infrastructure for builds on all architectures.
Side note: Regarding backports on CRAN, I have chosen to create a separate repository for R >= 3.4.0, so people should be conscious about the issue for R package debs when they install it.
