[SubjectToChange]

Writing another init system isn't exactly something most people would want to spend years of their life on. At best, it'd take a few years to reach some limited parity with where systemd is today. Furthermore, most of the systemd detractors fundamentally object the philosophy of systemd. So how can they meaningfully innovate over upstart and/or runit? It's either developing systemd-lite or a more elaborate ball of scripts. Even then, there is the issue of convincing distributions to adapt your new init system.

The reality is that systemd arrived at a time when Linux distributions were dying to move off of sysvinit. Poettering struck when the metal was hot and he delivered a comprehensive tool that greatly reduced the burden on maintainers. Sure, nothing lasts forever, but it will be many years (if not decades) before systemd is slated for replacement.