I think we could to make a list of things that could be redesigned, tweaked or simplified, besides the T12192, T12308, T12372, T12412, T10470.
* Discover
First of all i think that we could to overhaul a Discover, because it is one of the most important applications in Plasma space.
* KTorrent
* Okular
* KDE Partition Manager
This is very hard and incomprehensible app, GNOME Disks is much easier.
* KWalletManager
Firstly, this app has a bad name, it is more suitable name for personal finance application than for a tool to manage the passwords on your system.
* Sweeper