Some tools for these statistics;
For aggregate statistics; https://cran.r-project.org/web/packages/dlstats/vignettes/dlstats.html#introduction
Based on CRAN and bioconductor downloads.
We also query all R-user, R-ladies, satRday and other R-user group that use meetups.com via the meetupr package to build the events update. Upcoming R Community Events (from 2019-06-04 to 2019-06-15)
You might use data there with attendance numbers as a very rough estimate. Though, R is popular in universities, and fewer university R-user-groups use meetups.com.
It's a tricky problem since there are a few large groups of users that interact with these measurement tools in inconsistent ways. For example there are hundreds of thousands of new students each quarter using R for a stats or applied stats class. Then there are many others using R in academia, government and industry.