This currently missing are better LSP (Language Server Protocol)[1] (it supports only some of the LSP features), better linter[2] and static analysis, better integration with GitHub[3], and so on. More on the tooling side, I believe.

[1] https://cran.r-project.org/web/packages/languageserver/readm...

[2] https://github.com/jimhester/lintr

[3] https://github.com/github/semantic/issues/382