GHC seems to be more of a platform for crafting your own language than rust. Yes, rust nightly has experimental features that can enabled, but they seem to have gone through more vetting and design, whereas in GHC the features seem to be much more exploratory, or more explicitly, research oriented. It seems as though every contemporary haskell program is written in a different language, though rust at least, always has stable, which seems a much more sensible default than GHC's.