Ubuntu developers and KDE developers have co-exist with both Unity 8 and KDE, allowing users to have two desktop environments on the same system.
Currently the Unity 8 is still on a massive scale, so far the environment can be used on Ubuntu phones, the development of Ubuntu Desktop version is also actively developing, will be used in the desktop version as soon as possible. The Unity 8 and Mir display servers will fuse the desktop and mobile systems.
KDE developers must develop default desktop environment packages for each system, including Ubuntu.
According to the information provided by Michael Hall (a Canonical developer), Unity 8 and KDE can coexist as Plasma mobile system built on the Ubuntu SDK, using KDE as the default. The login manager also needs to make some changes, but nothing is impossible.
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Unity 8 and KDE can coexist in the Ubuntu desktop version