One of the key points of Plasma is while giving a simple default desktop experience, not limiting the user to that single, pre-packed one size fits all UI.
Its strength is to be flexible to greatly different user needs, “Simple by default, powerful when needed”.
Several years ago, the Visual Design Group had the idea of making easy to build and share desktop layouts to make easy to test wildly different user interfaces, see this old post by Thomas on the topic.
Since then, work on it has been going on, mostly on the infrastructure needed to make it a reality, and in Plasma 5.8 the first pieces are there, tough still far from the complete experience we want to offer.

The support for Look and Feel packages is there since a while (5.3 or so) that’s what one of those package can do:

• Provide a default layout for when Plasma starts for the first time, it was used for distributions to personalise their UI, but now is easier for users as well.
• Provide some default look options, like what color scheme to use, what icon theme etc
• (advanced) provide the actual implementation of some UI, such as KRunner, the Alt+Tab window switcher dialog, the lock screen

So far the default Plasma layout provided by the Look and Feel theme was used only when starting up for the first time, on a clean user home (therefore very useful for distributions) but sice Plasma 5.8, in the Workspace theme -> Look & Feel section of system settings there is an option to load the new layout when switching the look and feel theme. Not as default as is a destructive action that will remove your current Desktop setup.

The other component is a tiny little application shipped in the “Plasma Sdk” package that’s called lookandfeelexplorer.

With this applciation you can:

• Create a new Look and Feel theme
• Edit the metadata and thumbnail of a locally created/installed theme
• Create a default javascript desktop layout based upon your current Plasma setup
• Create a defaults file based upon your current setup as well, such as color scheme and icon theme

The last two are the central part of sharing your idea of “the perfect desktop” with others, linked with the integration between the Look & Feel systemsetting module and the KDE store, also new in Plasma 5.8.

It’s still a preliminary feature, as ideally in the future if your shared Look & Feel theme depends for instance from a particular icon theme or a particular 3rd party plasmoid, the store integration will download those dependencies as well.