You can try to install a software. If something does not work you can give me about it.
I actually already tried to install several versions of kubuntu : kubuntu-desktop, kde-full, kde-plasma-desktop, kubuntu-full...
Of course, none of the packages are referenced into the installed ppa.
Then I tried to install various ppa, but I got nowhere since the packages python-software-properties is not installed (an can't be installed for some reason)... I also tried the software-properties-common... which seemed to install properly, but which did not allow me to go further anyway...
I am pretty sure that if I could install a reasonably complete kde/plasma desktop, that would be a good starting point. After that, it is just a matter of adding the appropriate ppa for each additional software.
The "bug" seems to be with the initial addition of kde.
As mentioned in my first message, I was able, at some point, to achieve that result (as well as add a good number of applications which can be used in a Middle/High school environment) staring from the Lubuntu image, and the synaptic tool. So, I KNOW it can be done, and the result was very encouraging on the Banana Pi (still surprisingly reactive for such a small machine). But that wasn't particularly "clean" or optimized. I also had a strange problem : access to the tool that lets users add widgets would be "locked" : it would open, but it would not react to the input devices (keyboard or mouse)... Hence my idea of starting from your image, which should be cleaner.