Edit: To add a bit more to the conversation, does the change from Canonical to Blue Systems[2] changed much to the development of Kubuntu/KDE?
[1] https://2.bp.blogspot.com/-asFPvnoidnw/U4cXbGCcv2I/AAAAAAAAM...
Blue Systems OTOH is a big KDE contributor. Things like KDE Search improved a lot thanks to Blue's involvement. As for Kubuntu: It appears to me that mostly the same people are involved with it. The only KDE thing mostly specific to Kubuntu is Muon (and that's being ported to Debian as we speak). Everything else by Blue Systems is AFAIK cross-distro.
The Kubuntu guys already announced that Canonical's own display server Mir is not an option. Therefore it remains to be seen how feasible Kubuntu remains with Canonical pushing a Wayland competitor.
KUbuntu = Worst KDE integration and the cause for why so many people have a negative view of KDE!
OpenSUSE = Best KDE integration
Take `zypper se -s`, for example - or if you prefer the long form, `zypper search --detailed`. How do you get that information from any of the apt tools, or even aptitude?
And then there's the openSUSE build system.
But I digress. I will attempt to replace my openSUSE installation with NixOS and if I miss my automatic KF5 builds, I'll try to create Nix packages for them.
Zypper is by far my favorite package manager and find apt-get and company a PAIN. apt-cache search foo UGH!