Area 51 is the Stack Exchange site for proposing new Stack Exchange sites. If your idea for a new site comes from observing commonalities among off-topic questions on Cross Validated, it'd be sensible to discuss it first here on CV's Meta & to link to your proposal if you decide to make one.
Your example—questions involving R—has been much discussed. As @AndreSilva points out, there was a proposal for an R Stack Exchange site, but it didn't go anywhere. Currently we welcome questions that arise from using R, or other statistical software, on Cross Validated when they're statistical questions. (Understand "statistical" here in a broad sense—encompassing machine learning, data visualization, &c.) The majority that aren't are programming questions, & have a home on Stack Overflow, as @NormalHuman points out. A minority are better suited to other Stack Exchange sites (see e.g. https://askubuntu.com/questions/tagged/r). Some fall into a grey area where it's not clear, perhaps not even to the person who asked it; many of us try to encourage & facilitate the asking & answering of questions in a software-agnostic fashion. We also maintain a collection of links: Internet Support for Statistics Software.