Love this! I did this in 2020 and until today I hadn't seen anyone else who had done it. If anyone is tempted, I recommend finishing the job with Micro-Mesh. IIRC, I went up to 12,000 grit and it results in a nicely polished look that catches the light beautifully.[1] I bet it would look even more striking on the actual black MacBooks we have today.
[1] https://x.com/andrewculver/status/1297575768520716288/photo/...