Nice suggestions, @felixernst!
Since my semester break is about over, I won't be able to do much about them for some time, though.
Also, let me cross-link some related mockups by @aronkvh: https://phabricator.kde.org/T14933

I really liked this idea, so I tried making it a reality. I'm a QML/Kirigami newbie, so neither the UI nor the code look amazing, but – it works!
https://github.com/NicoWeio/Produktive