Has someone here by chance written a pre-SRFI for macroexpand (or
macro-expand, syntax-expand, etc.)? Would be nice to have a standard way
to find out what code your macros expand to.

Since Scheme has several macro systems (syntax-rules, syntax-case,
CL-style define-macro, maybe others?) does that complicate the interface
of a macroexpander, or is the complexity all in the internals?