Scheme is in recent standards (since R6RS) divided in two: a core language, suitable for reasoning about, and a full language, aimed at expressing economically the kind of solutions software engineers come up with. The full language is meant to be expressed in terms of the core language.

This seems analogous to the two-language approach you describe for Algol 68. Are you aware of recent developments in Scheme? Your description of it characterises it as a ball-and-chain for Algol 68.