FWIW that's not an official move by CRAN, it's just an interested individual mirroring all CRAN packages

Sort of disconcerting that R is somewhat flat in terms of its growth though.

I think there's steady growth in active R repos that's masked by the huge impact of Hopkin's Coursera course on reproducible research. Tens of thousands of people fork a repo for a homework (https://github.com/search?q=forks%3A%3E30000&type=Repositori...), and then never touch it again

I would imagine that this is because R is a language that is more used for a specific purpose rather than a language that is developed.

Part of that is the fact that many R packages are actually predominantly written in C++, C, Java, etc..., so they show up in Github searches as being written in a language other than R...