Unable to locate package kubuntu-plasma5-desktop on 14.04

If you're using 14.04 (per the revised question)...

The ppa:kubuntu-ppa/next PPA has no Utopic build. It's designed for the development version of Ubuntu and nothing else. Remove it:

sudo apt-add-repository -r ppa:kubuntu-ppa/next

By extension the kubuntu-plasma5-desktop package only lives in this PPA so you're not going to be able to install that yet.

Just use the Neon version in ppa:neon/kf5 (which only works for Trusty). As the blog announcement for all this states:

Packages will be installed to /opt/project-neon5 and will co-install with your normal environment and installs to 14.04

Once you've installed project-neon5-session, project-neon5-utils and project-neon5-konsole you should be able to choose Neon as a desktop session from the login screen.

If you're using 14.10 (per the original question)...

The neon/kf5 PPA is only intended for 14.04 Trusty. It doesn't have packages for Utopic. Remove it with:

sudo apt-add-repository -r ppa:neon/kf5

The kubuntu-ppa/next PPA should work on 14.10:

• It has a Utopic build target.
• Looking at the Packages file, it does have a kubuntu-plasma4-desktop file.

If it's not working, check the output of sudo apt-get update (use apt if you like) and see what that's saying. Any warnings and errors about the second PPA are going to be relevant here.