@lhp @astrid @dushman Personally I'm not so fond of a number of things about Scheme, but a few in particular are most relevant in this case.

The Scheme standards have effectively no provisions for dynamic introspection, which is a problem when one wants a long-running environment where such introspection capacity would either require adding nonstandard mechanisms (RIP portability) or foregoing them (unacceptable feature degradation).

> used more system libraries (slowly getting there)

That is a good thing exclusively for those libraries which are portable across systems, otherwise it represents a ball & chain for Emacs.

> and shipped less lisp code by default

Destroying Emacs' dynamic reprogramming and modification is a likely outcome of that (particularly given how bad the current Scheme implementations are at it, so even providing a separate REPL to the underlying Scheme isn't enough). That defeats the majority of the point of using it as far as I'm concerned.

I would sooner prefer an Emacs implemented fully in Common Lisp or Interlisp (if one must absolutely avoid CL for whatever reason).