Plasma 2014.6 is a whole new version and won't co-install with Plasma 1. Nevertheless some parts of runtime should co-install so apps using kdelibs4 can run under Plasma Next.

not co-installable

these overlap with KDELibs 4 equivalents from kde-workspace, no change expected

libksysguard
ksysguard
kinfocenter
kmenuedit
kwrited
systemsettings
khelpcenter
powerdevil

kde-cli-tools

clashing files with kde 4's kde-runtime: https://git.reviewboard.kde.org/r/117884/

kwin

No reason why this needs to co-install but Martin asked. Clashing files with kde4 kwin:

/usr/bin/kwin (due to be renamed?)
/usr/lib/x86_64-linux-gnu/libkdecorations.so
/usr/share/doc/HTML/en/kcontrol/windowspecific

Oxygen

liboxygen/ clashes and should be renamed https://git.reviewboard.kde.org/r/117770/
kstyle/ oxygen-settings and oxygen-demo should be renamed DONE
cursors/ all clash and should be renamed (or removed, why do we ship multiple cursors?) https://git.reviewboard.kde.org/r/117856/
kwin-decorations/ oxygen-shadow-demo should be renamed https://git.reviewboard.kde.org/r/117773/
sounds/ should all be renamed https://git.reviewboard.kde.org/r/117775/