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

kde-cli-tools

clashing files with kde 4's kde-runtime:

/usr/share/man/man1/kdesu.1
/usr/share/doc/HTML/en/kdesu/index.docbook
/usr/bin/keditfiletype
/usr/share/kde5/services/filetypes.desktop
/usr/bin/kmimetypefinder
/usr/bin/ktraderclient
/usr/bin/kioclient
/usr/bin/kdecp
/usr/bin/kdemv
/usr/bin/kde-open
/usr/bin/ksvgtopng
/usr/bin/kstart

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
libkwinglutils.so.1 (needs sobump anyway?)
libkwineffects.so.1 (needs sobump anyway?)
libkwinxrenderutils.so.1 (needs sobump anyway?)
kwin_update_default_rules can be removed
/usr/share/sounds/pop.wav
/usr/share/doc/HTML/en/kcontrol/windowspecific

Question: why did kwin.png and kcmkwm.png move from apps to actions? They might need renamed apart from this.