took the step and dared to upgrade a live system from Kubuntu 16.04 to KDE Neon 5.9. I didn't do a clean install to save work.
Again it turned out after several update/upgrade cycles, and force install neon-desktop with sudo apt install neon-desktop -f , the system rebooted without issues and I could go on. I still get 2 error messages regarding korcag and kgpg. The first issue doesn't seem to have something to do with the upgrade and the kgpg is to be investigated. Since the major programs like kdenlive and the multimedia players works, it seems to be consistent so far (fingers crossed). No dependencies left over.
I like what I see on the new Plasma desktop and I like to have the latest version of KDE running on top of a stable LTS base. So while the KDE team says that KDE neon is not a real distribution, for me it is and should be presented like it. Let's see how this works out over time. For now my needs are satisfied.
To be honest, most of the time, I'm not even running Plasma, since I use i3wm. But I use programs running on KDE, like the mentioned kdenlive and sometimes dolphin (but I like dired-mode in emacs). And the underlying structure is also used for kdeconnect and Konsole. Even those really bothered me when out of date. I can't understand that people think "stable" means "outdated". Stable is the newest thing that works. It does not mean you should get only security patches. Everything that is unstable is beta and has nothing to do with new features! Sigh...