> Which is Canonical's problem, and no one else's.
It then becomes the problem of its users, and rapidly the problem of userland developers, because users expect their software to just work in Ubuntu.
Developers can now go and waste effort just to comply to Canonical's de facto walled garden, or lose all Ubuntu users (furthering the "Linux is too complicated and fragmented!" narrative).
Assuming binary-only distribution, you already have this problem for a multitude of distros. If you're employing such a proprietary model, you'll obviously have problems you'll need to overcome.
Assuming source distribution, I do not see any special effort required.
For the record, most projects do not supply configurations for every possible userspace plumbing, but either none or only select ones. Upstart jobs would be written by the distribution maintainer or user. Mir hasn't even rolled out yet, and IIRC it has X11 compatibility anyway. Why would you need special effort to support Unity other than a .desktop file, which is interchangeable with GNOME (Unity reuses GNOME under the hood)? Kernel and libraries do not require special effort at all to support when distributing source.
It's also funny how people routinely bitch about Upstart when it predated systemd.
It then becomes the problem of its users, and rapidly the problem of userland developers, because users expect their software to just work in Ubuntu.
Developers can now go and waste effort just to comply to Canonical's de facto walled garden, or lose all Ubuntu users (furthering the "Linux is too complicated and fragmented!" narrative).
Everybody loses, nobody wins.