Some additional discussion appeared in the pre-PEP thread, starting at "Solid bases" for detecting incompatible base classes - #13 by jorenham . Let’s move any remaining discussion to the PEP thread.
The main point that came up was the name. I picked the name “solid base” because that’s the term used in the CPython implementation. It’s been there for about 25 years, but the term did not appear in documentation or error messages until I added it recently (8. Compound statements — Python 3.15.0a0 documentation).
As an alternative, “disjoint base” was suggested. “Disjoint” is a good term because two distinct solid bases are disjoint from each other, in the sense that they cannot share a child class. Thoughts on using “disjoint base” as a term for the feature and @disjoint_base for the decorator?