So, I used to vaguely help develop another proposed init replacement a few years ago, and it's entirely correct. The only way to upgrade init is to have it dump state and re-exec() itself, and there are theoretical failure modes that will cause init to crash before it's even possible to set up a crash handler to catch the problem, causing a kernel panic.
What's more, supporting upgrades this way means you need to support every previous state file format, and the more state and features there are the harder this is to do. (Seriously, it was a pain in the butt to keep track of.) systemd is developed primarily by and for Red Hat who avoid this problem by not supporting upgrades to a new distro release from within the running system - but most other major distros do and will likely be bitten hard by the issue.
Without support for this you can't even reboot cleanly after upgrading init or any of the libraries it uses, because init will keep old deleted executable open and make it impossible to remount root as read-only (an obscure quirk of Unix filesystems that basically only init developers need to know). You don't just need to reboot to upgrade init, you need to boot into a special upgrade environment that doesn't use the system's init, and Fedora does. That's why Fedora needs daemon-reexec - otherwise they wouldn't even be able to apply security updates to glibc without rebooting first. Compare this with kernel upgrades, which can be installed immediately and simply don't take effect until the next reboot.
Without support for this you can't even reboot cleanly after upgrading init or any of the libraries it uses, because init will keep old deleted executable open and make it impossible to remount root as read-only
Lennart Poettering on how this is done in systemd:
That's quite a clever solution - except that upon reading what Lennart says in the comments, systemd-shutdown is apparently closely coupled with systemd and receives enough state from it that it cannot be used with any other init system. So I'm not sure it's safe to rely on that for any major upgrade. (Not entirely sure why it needs all that state either.)
Java SE. Scala. Kotlin. Groovy. Clojure. If it's on the JVM, it works. (If you are expecting to use it for application-server development, there's no problem in expecting enterprisey-you to pay the man.)
The awesome Chrome extension Hacker News Sidebar, which uses searchyc.com, is down too.
Are there any alternative extensions or bookmarklets for automatically linking a page to its HN comment thread?
This is not needed anymore. Check systemd's manual for 'systemd daemon-reexec'