KDE will not support Mir as long as it remains a one-distribution solution. With KDE not coming to Mir for the foreseeable future, Jonathan Riddell of Kubuntu started a new technical discussion about non-Unity flavors and Mir.
Basically, the options now for Kubuntu (and similar derivatives like the LXDE and Xfce versions) is to either use Mir, use Wayland and hope everything works out, or simply end of life the distribution. Jonathan on the behalf of the Kubuntu development community is hoping that using Wayland will work with Debian packages and that it will be able to co-exist with Mir. Using Mir really isn't acceptable since the Mir KDE support won't be accepted upstream and the developers have limited resources.
The discussion so far today on the mailing list is pretty much as expected with much uncertainty still existing about Mir outside of Canonical. Thomas Voß of Canonical, one of the Mir developers, did express possible interest in seeing about integrating KDE/KWin support onto Mir anyhow, if he's able to obtain some KDE guidance.
The only other news out of this discussion so far is that there's likely coming a forum for all Mir stakeholders (other ISVs, etc) to discuss issues and drive alignment around this Wayland competitor.