It's not just a release date issue. It matters (to me, at least) that Canonical was doing it's thing, RH invents something shortly after that trounces Canonical, Canonical makes futile attempts to save the ship before finally dumping the project.
For example, Upstart. RH invents SystemD, Canonical stays with Upstart until, like, 2017 before giving up.
systemd's widespread adoption was somewhat controversial and took years. I realize Upstart didn't receive widespread adoption, and Canonical has historically liked to start its own products (Mir and Unity as you noted). But the discussion around systemd was not "everyone except Canonical thinks it's good", and Upstart had been in development for several years.
Wasn't it Canonical creates Upstart, switches Ubuntu to it, RH switches to it; a few years later, RH creates SystemD, RH switches to it, Ubuntu switches to it?
Nah, they could have maintined Upstart integration like they did before. The number of packages that need init system integration is tiny compared to the whole of Debian.
> Red Hat did use upstart before adopting systemd FWIW
RHEL added support for Upstart as a hybrid with SysV, however it was never heavily used and not by most of their own packaged RPMs. Spin up a CentOS 6 server, install a bunch of daemons then go compare /etc/init/ to /etc/rc.d/init.d/.
But the init system was Upstart. Upstart, like SystemD, can start daemons from SysV scripts. At the time, the majority of distros still used SysV or SysV-like init systems. As long as the newer systems had backwards compatibility with the SysV scripts and the newer functionality were not needed, why would upstream switch to the new format?
SystemD has managed to gain near-ubiquitous usage, to the point where plenty of upstreams now only ship systemd unit files, but I would argue that this change was first initiated by the introduction and adoption of Upstart in both Ubuntu and RH.
We tried to use Upstart properly in Fedora. We spent three Fedora releases trying to do that (Fedora 9, Fedora 10, Fedora 11, and Fedora 12). We gave up by Fedora 13.
Snap: Loved only by Canonical devotees. Zero distros supporting Snap exclusively by default.
Red Hat: SystemD
Canonical: Upstart, dead to SystemD.
Red Hat & Others: Wayland
Canonical: Mir. Dead to Wayland.
Red Hat & Others: GNOME 3
Canonical: Unity1-7. Dead to GNOME.