You might be interested in the Cerberus design: https://www.thebyteattic.com/p/cerberus-2100.html?m=1 https://www.thebyteattic.com/p/cerberus-2100.html?m=1 It

You might be interested in the Cerberus design: https://www.thebyteattic.com/p/cerberus-2100.html?m=1 https://www.thebyteattic.com/p/cerberus-2100.html?m=1 It doesn't match your concept precisely but it has concretely implemented a good combination of observability and capability - graphics, sound, keyboard support. The BASICs can be safely ignored in favor of Forth, which goes directly to the point of tangibly understanding the machine - Forth programs are already structured code, interactive, with extensible syntax, but they also let you crash the computer in moments with a bad memory write. The pedagogical value is immense within an 8-bit environment.