David Edmundson, who for a long time has been working on LightDM and has led when it comes to LightDM-KDE, wrote an interesting blog post this morning about how Mir conflicts with LightDM -- the display manager that's also used by Ubuntu.
In summary, LightDM developers were/are planning for Wayland support. LightDM is worked on by Canonical and others while the Qt library used by LightDM is controlled by Edmundson. "The Qt library was originally only used by us and Razor Qt, but with Unity's move to QML this means that Canonical are now dependant on the libraries I made. I am still in charge of the Qt library and still get final say on all reviews, I have rejected some Canonical employee patches as needing a rewrite and them with some of mine, it feels like a real open meritocracy community."
The part that Edmundson is now mad about is that Canonical never informed the LightDM developers in advance about their plans to use Mir and not continue their plans to transition to Wayland, which they had been promoting for the past two years. Mir was in development for the past half-year but never informed the open-source community developers who were expecting Canonical to plan around Wayland. "If I'd known they weren't going to add Wayland support, I'm not sure I would have invested my time in LightDM. I don't feel decieved, they thought they would do it at the time and Canonical are perfectly within their rights to decide to do something else. The problem for me isn't that Canonical changed their mind, but that they didn't (or the developers weren't allowed) to tell me! If you know for 6 months that you're not going to do something you said you would it's rude not to tell people. It now sets our schedule back and that's really really frustrating."
LightDM developers will need to add Wayland support themselves now rather than relying upon any Canonical contributions. It sounds like this will still happen though since the Linux desktop community will soon need a display manager that works with Wayland and Qt5.
David Edmundson's blog post can be read in KDE, LightDM and the Mir Kerfuffle.