A YouTuber has managed to shrink the current Mac mini by almost two-thirds without compromising on the performance that the Apple M1 offers. While Apple is unlikely to ever take this radical approach with the next Mac mini, it shows what could be done if Apple paid closer attention to optimising the space within its mini-PC.
https://www.notebookcheck.net/Apple-Mac-mini-YouTuber-demonstrates-that-the-Apple-M1-mini-PC-could-be-nearly-two-thirds-smaller-than-its-present-size.605692.0.html