At some point remembering keyboard layouts through sessions was implemented, right? I recall seeing this work on Kubuntu, but on openSUSE it does not.
Is it really implemented, is there an option for that somewhere?

By through sessions, I am guessing you are referring to between sessions. I am not sure what would be needed to make it work - however it is possible that different distributions run different commands as part of their startup/shutdown scripts for desktop environments, which could be preserving this state.

Yes, I mean "between sessions". Wasn't it done in some KDE release like THE way? I remember reading sometime somewhere something about it

This perhaps may have changed when the new keyboard layout manager was merged in - however that was at least a release or two ago from what I recall (it should be in KDE 4.9 at least).