Casey Muratori (of Handmade Hero fame, works/worked at RAD Game Tools for a long time) just did that as part 1 of his Performance Aware Programming series he’s doing on his Substack: https://www.computerenhance.com/

The “homeworks” only require implementing basic data transfer, arithmetic, and logic instructions, but I enjoyed it so I implemented everything except the interrupt handler stuff (into, etc.), and the BCD stuff (aaa, etc.).

I agree that it’s a good way to learn, and Casey provides a reference implementation.