"I'd much rather have seen it built around scheme, [...]"
It's not meant to be built around any language. If there's a language you want to use, just start using it. All you need is access to the system calls. The whole point of making everything a file system is so that you don't have to cram everything together in the same address space. There's no foreign function interfaces or calling conventions you have to deal with if you want to use a new language with the system. It's all reads and writes. Ocaml, Haskell, and ML all have read and write, so if you want to use a less primitive language, there's nothing stopping you.
It's not meant to be built around any language. If there's a language you want to use, just start using it. All you need is access to the system calls. The whole point of making everything a file system is so that you don't have to cram everything together in the same address space. There's no foreign function interfaces or calling conventions you have to deal with if you want to use a new language with the system. It's all reads and writes. Ocaml, Haskell, and ML all have read and write, so if you want to use a less primitive language, there's nothing stopping you.