Or dinit. dinit is awesome. s6 defeated me; an init system shouldn't be that complex.
systemd has a lot of nice features, esp. in the area of dependencies and triggers. But it infects everything it touches, is enormous, and is buggy.
Frankly, I'm waiting for the PipeWire successor to systemd. Like systemd, Pulseaudio was everywhere by the time enough people realized how bad it really was and someone wrote a well-designed, well-written replacement. ALSA has problems that Pulseaudio fixed, but with a badly written solution; then a good software developer came up with a good solution that solves the same problems but isn't just a giant hacky hot mess and now PA is slowly being replaced everywhere. Given that the same person, of questionable skill, who wrote PA also wrote systemd, I fully expect a better-designed solution to replace systemd.
S6 isn't it. dinit is close, but has some holes that need addressing before it could succeed systemd, and I think it won't be it; I think systemd's successor hasn't been written yet, but I have confidence it will be.