This topic is very old and tbh my motivation was very low to start it again, but as the feedback from the akadamy was that the plasma team want to start with this topic again, I'm motivated again.

There are some options how to manage this task
1. wait for kuserfeedback results to found out which kcm's are importend for the users
At my university I make the student documents new. 400 latex pages. before everything was in word. after the first year we get a lot of feedback from the students (orthography, smaler stuff, ...) and in one chapter the students told as that the calculation was wrong. the calculation was also wrong in the old document, but in the old one, nobody understood it and so nobody read/use it.

2. update one KCM after the other
This was the idea in the last > 3 years, where not that much happens. Sometimes it is good to focus on one topic, like plasma hade a bug hunting release. In addition there is a HIG for KCM's and the VDG is always willing to support but only one KCM was renewed in the last 3 years. The Desktop Theme KCM. It was writen in 2 days, than some time of bughunting and it was in the next release.

3. update all KCM
This task is HUGE we are talking about 70 (by default installed KCM's) and additionally some other KCM's. Update all KCM's would be a big (maybe to big) step. So I separte the KCM's in the 4 major sections
- 1. Appearance
- 2. Workspace
- 3. Personalization
- 4. Hardware

For 1. Appearance I have a final draft in the VDG share https://share.kde.org/index.php/s/w0gpfnHtoY6zNCi 
Feel free to comment. I use the nextcloud share cause there I can add the svg files, an general writer file with the description and the images. The discussion is in the KCM telegram group. If you prefer another communication tool (phab, forum, ...) no problem.

2. Workspace is in general 80% window manager. as it was already written this task is not that easy, but I prefer to make one section after the other cause than it's general easier. e.g. the Virtual Desktop KCM has a tab with Switch effect and shortcuts. From the user point of view it is "nice" to have the shortcuts in the VD KCM, but there is already a shortcut KCM so if this KCM would work better (KWin has the option to define 160 shortcuts in the GUI), separate the Virtual Desktop specific shortcuts wouldn't make sence. Same for Desktop Effects.

I make a icon theme for LibreOffice with 3.500 Icons in 3 mounths with the help of Uri. Nobody else did this task in the past. I like big tasks and I can wait when the implementation need longer. It is way easier to develop after an well designed and finished (discussed) KCM mockup than without.

Please join the journey to a better System Setting.
Andraes_K

document share:
https://share.kde.org/index.php/s/vadAnAoVp14zwaE