The R programming language is a rapidly developing language which gained lots of new users in the last years.
Coming from the statistical field, its scope has expanded nowadays. Especially the usage in an academic context increased in the last years. R is also used for writing books, creating professional reports, developing UI applications or performing machine learning tasks.
Organizations like ropensci or r-lib are great examples of immense open-source effort to advance the R community.
Besides these, many developers started developing packages (> 10k open-source packages exist) in the last years and see the need for a CI testing suite.
Until now, there is only support for R on Travis CI.
I see a lot of advantages in how Circle CI runs builds compared to Travis CI. Hence I would love to see official R support for Circle CI. Among others, this additions would result in reduced build times due to the existence of a cached docker image.
Furthermore, having a second CI provider for the R community would give the R community more flexibility regarding their CI provider choice and also put some load off from Travis CI.
There have been recent efforts to optimize the support for Circle CI within the R community. Examples are packages like tic or the API-client package circle.