Hi! Sorry if this is not the right thread for this or if this was suggested before.

I found the proposed content structure here.

There are two palces to tweak appearance settings:
Common Appearance and Behavior -> Application Appearance
Workspace Appearance and Behavior -> Workspace Appearance

Newcomers don't know the difference between "Common Appearance" and "Workspace Appearance", so some them will go to "Common Appearance" to change Plasma theme.

I am proposing to have a note somewhere in "Common Appearance" dialog window: "Related settings: Workspace Appearance", where "Workspace Appearance" is a clickable link.

I think other settings pages can also have something like: "You might be interested in these settings too: ..."

I might have misunderstood (it does happen sometimes ), but the diagram of the new structure shows two columns:

Left column - The old structure as it was before it was reorganised (so as it was in KDE 4.x & before)
Right column - The proposed new structure

The dashed lines between the two columns show where each module has gone in the new structure. In the new structure the categories (top level groupings) Common Appearance and Behavior & Workspace Appearance and Behavior and their KCMs have been reorganised more logically, so now we only have the Appearance category for pretty much all the appearance related KCMs.

Ah, yes, my bad.

Still, I think that showing link to other related settings could be a good idea.

For example link to Hardware -> Display and Monitor -> Compositor in Desktop Effects.

This kind of thing is a good idea - it was suggested by Heiko, it's been called See also and is missing from the screenshots on the proposal you linked to 3 posts ago but if you look back at some of the mockups in this thread it's at the bottom of the side bar when you're in a KCM - see this screenshot:

It's missing from the screenshots on the proposal but it is mentioned in the text as See-as-well (just my opinion but i prefer See also).

There's a thread about it here:
viewtopic.php?f=285&t=125224

Great! Thank you.