RedHat is moving to systemd, and Oracle will follow suit because they base their distro on RHEL.
Regardless, Upstart is hardly comparable. It's just an init system, and having a different init system rarely if ever affects compatibility of applications. The same cannot be said of a display system (except if we're talking about CLI applications). Mir will end badly for Ubuntu, they will be forced to at the very least implement client-side compatibility with Wayland - which would effectively make Mir another Wayland compositor. At that point, no one will bother maintaining Mir support, even if they did at that point (which is already unlikely) and eventually, Ubuntu will just quietly phase out the Mir API and just use pure Wayland only.
It's just a shame for all the damage they'll manage to do in the meanwhile.