Plasma 6 landed in opensuse. However, I recommend to do it in tty because if you do it in plasma the upgrade will be incomplete because the shell will crash in the middle of update without installing all. In case this happen to anyone, just reinstall plasma 6 pattern and it will go without problems
In my case I had another WM installed (iceWM, I think it was there by default?) and did the upgrade from there. Unfortunately it does seem that if you try to upgrade from within KDE it will crash part-way (I used zypper dup and it failed).