WASM interpreter from scratch is great not only because "omg livecoding interpreter from scratch", but also it is a lot of inspiration for hacking and exploring things.
I just came here to post this! Mindbogglingly great talk... Was lucky enough to catch it live at Pycon India.
Just watched this video. What a quality live coding: fast and low on bugs. Learned about stack based machines from very basics. Would upvote more if I could.