The goals distinguishing from other init systems seem to be:
- musl support
- guaranteed bootability
It's not easy to extract this from the post, since it's hidden between value statements like "flexible", "small", "fast", "unpredictable", which aren't defined anywhere, nor supported with external statements.
Since those aren't defined, it's also not clear why the author didn't decide to contribute support for the two defined criteria to systemd.