systemsettings5 correctly displays settings for KF5 applications, so it's just a question of more KF5 packages making their way into the archive. You can verify this by installing bluedevil (currently 4:5.3.2-1 in unstable) : a bluetooth icon appears.
I have also built kwin using the packaging in the Debian Qt/KDE Maintainers git repo, and the window decoration settings appear too. Cheers, Jeremy
