Mir is actually making a lot of progress, but I can also see why Canonical would want to create their own display server rather than use an existing one.
Part of it is NIH, but the other part is probably the lack of full integration and control they'd have with regards to Ubuntu. It's still open-source, and they're working hard on it. I don't see what the issue is.
The issue is that they bad-mouthed the competing project by making a bunch statements about short-comings that apparently don't exist. It would have been much better for them to just come out and say, "we want to create Mir so that we have control over it and can integrate it completely with Unity Next," but they didn't. See also the recent post on HN about Kubuntu + Mir/Wayland and the possible issues (and unresolved questions) about keeping Kubuntu going.
Well, Ubuntu definitely messed up on their arguments regarding Wayland.
That said, keeping Kubuntu going is not Ubuntu's responsibility. It may very well be that Kubuntu will need to fork off Ubuntu (or base off a different distro), and that's ok!
It's not their responsibility, but it's not going to generate a bunch of goodwill for the Canonical/Ubuntu though. If they came out and told people the real reason for Mir, and why they thought that they wouldn't be able to integrate Wayland and Unity Next (beyond NIH syndrome), people might be more understanding. Also, the biggest question mark for Kubuntu seems to be whether or not Wayland and Mir can coexist on the same system.
