Hi,
I’m a courious guy. I saw that KDE published a final beta of frameworks 5: http://kde.org/announcements/announce-frameworks5-beta3.php
There are even repos: http://en.opensuse.org/SDB:KDE_repositories#KDE_Frameworks_5_.26_Plasma_5
Did anybody dare to install that? Can it be done as an additional Window manager, besides KDE, i3, …?
No. It replaces kdebase4-workspace, i.e. KDE4’s desktop and window manager.
It was possible to install it in parallel (it got installed to /opt/kf5/), but that has changed recently:
http://lists.opensuse.org/opensuse-kde/2014-06/msg00006.html
So at the moment it’s either KDE4’s Plasma or Plasma 5.
Thank you, especially for the reference. OK, than I’ll have to wait for, hm, openSuse 13.3.
Well, three days ago it was still co-installable, you waited a bit too long… 
You could try out the “semi-official” Neon 5 Live ISO though:
http://neon.blue-systems.com/live-iso/