Unifying a few codebases, and make Plasma more modular.
1. A minimal Plasma
I think Plasma is the best desktop and suited for minimal installs on machines with like 2GB of RAM. Reducing the needed dependencies (currently working on that in Fedora) to the bare minimum. Making all the fancy desktop effects, animations, blur, transparency, floating, ... optional.
And yes, please also remove the default plasmoids from the needed install. Maybe keep the ones default in the panel. Maybe add a way to find them as "official plasmoids" which would help a lot.
2. Merge parallel works
Gwenview, Spectacle, Kolourpaint, digiKam all have image editing bars. The one of spectacle is pretty good, Gwenview and digiKam could be merged, Kolourpaint could maybe get an additional few things specific to the app.