Branch project for KDE:Frameworks5
This project contains Plasma 5 packages that don't conflict with kdebase4-workspace or the corresponding KDE4 applications' packages, so can be installed side-by-side with KDE4 (they install to /opt/kf5).
Install plasma5-session to be able to select Plasma 5 on your Login Screen, and/or plasma5-session-wayland for Plasma/Wayland (not supported by kdm though).
Also it contains KDE4 packages that are no longer available, are crippled, or KF5 based in the standard repos.
Install kdebase4-session to get a "KDE Plasma Workspace" (i.e. KDE4) entry on your login screen (this should also pull in all necessary packages for a basic KDE4 desktop).
Please note that you also need the KDE:Frameworks5 repo (and additionally KDE:Qt5 on Leap) for neccessary packages!
This project only contains versions of those packages from there that conflict with KDE4.
Exception: The Tumbleweed repo is built against plain Tumbleweed, no additional repo needed if you use that one.
You should probably give this repo a higher priority (= lower priority number) than KDE:Frameworks5 and the standard repos, especially on Tumbleweed, to make sure the packages from here are preferred.
And it's advisable to do a full switch to this repo (and KDE:Qt5/KDE:Frameworks5 if applicable) after you add it, to rule out a mixture of packages, especially if you already have a KDE installation. See https://en.opensuse.org/SDB:Vendor_change_update ("Full repository Vendor change").