Obviously it fragments the language in a way that's harmful for human readers as well as software like compilers, editors/IDE plugins, and so on. How to know wh

Obviously it fragments the language in a way that's harmful for human readers as well as software like compilers, editors/IDE plugins, and so on. How to know which variant of Rust you're reading? As you add more options that change the syntax and semantics of the core language, these difficulties will be compounded. Maybe a bit of fragmentation isn't the end of the world, but I think you'd need a really good argument in its favor and in this case frankly I don't see one. Additive extensions/features (like GADTs in Haskell) are an easier sell for me because a) they actually add something useful and b) they generally don't change the core language, but rather sit on top of it.