Maybe 3-4 years ago there was a big push to speedup R by replacing the runtime; at least 3 competing replacements were talked about pretty actively. None of them achieved much mindshare. R trades runtime speed for dev speed, and we juice performance by writing slow stuff in C++ and linking Intel's MKL. The RStudio folks are also making the low-level stuff faster and more consistent through the r-lib family of packages, which are awesome.
Big barriers to adoption here: not a truly drop-in replacement, R people have an aversion to Java (we've all spent hours debugging rJava; luckily most of those packages have been rewritten in C++ now), and nobody likes Oracle.
I think the best-case scenario here is that progress on FastR pushes the R-Core team to improve GNU-R.