Canonical never contributed much to KDE. Yes, a few bits here and there but overall mostly negligible.
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.
Last time I used KUbuntu it was pretty much horrible. (E.g. only 6 month maintained and after that the repo did go offline so my installed system was broken (couldn't even install old pkgs from the DVD because of dependencies)). But the config tools from SuSE where also horrible (convoluted and so slow!), so I use the Fedora KDE spin now.
Having used both zypper and apt-get, I find the latter very lacking, even when coupled with other tools.
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.
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.