Ubuntu – How to remove KDE desktop from Ubuntu

I think plasma-desktop would best fit your needs

Provides the environment for running and managing applications and integrating interaction of applications. It is designed as generic environment for all kinds of desktop applications, not only applications built on the KDE Platform. It integrates best with applications following the standards used by the KDE Platform.

Ubuntu Stable Release Updates

https://wiki.ubuntu.com/StableReleaseUpdates

Stable release updates are automatically recommended to a very large number of users, and so it is critically important to treat them with great caution. Therefore, when updates are proposed, they must be accompanied by a strong rationale and present a low risk of regressions.

Kubuntu Backports

https://launchpad.net/~kubuntu-ppa/+archive/backports

PPA description

Backports of new versions of KDE and major KDE apps for Kubuntu which are either too large a change or not yet tested enough to go to Ubuntu Backports.

I think that the new version of the KDE is in the "too large category". The new backported KDE version is also build against the new version of the Qt.

Q&A

Can I trust this PPA?

The packages are backported by the same Kubuntu developers who are building the Kubuntu 12.04 packages.

But there is always the risk ( https://help.ubuntu.com/community/UbuntuBackports ):

When using Backports, it is important to understand that there is an inherent risk in backporting software. Although backported packages are tested by the community before they are included in the repository, there are very occasionally bad interactions with the older software on your system that are overlooked...