The story of KDE's user revolt is well-known. What is less well known is that, in the six years since then, KDE has been steadily regaining its user-share.
In fact, for the last few years, KDE has registered as the most popular desktop among experienced users. Despite the obvious limitations of reader polls, they show KDE's popularity consistently well ahead of Xfce, the usual runner up, in2011, 2012, and 2013 in LinuxQuestions' Members Choice Awards and in Linux Journal's 2013 Readers' Choice Awards. Even assuming a wide margin of error in the polls, the consistency makes KDE's recovery hard to question.
What are the secrets behind KDE's comeback? I count at least nine design guidelines, some of which may be unofficial, and others that are at least working guidelines, if not official policy, for the development team.
The current KDE release series implements the standard features of a classical desktop in different ways. For example, adding icons is not a matter of using the desktop's context menu, but of adding a Folder View widget to the desktop.
However, despite the change in implementation, the feature of a classical desktop remain, and are not discarded in KDE the way that they are in Unity or the default installation of GNOME. Other major changes, such as Activities, are added on top of the classical features, rather than replacing them. This arrangement allows users to choose whether to ignore or accept changes rather than being forced to accept them.
KDE does sometimes replace old features with new implementations. For example, Activities might be said to make virtual desktops obsolete.
However, instead of removing virtual desktops, KDE continues to have them co-exist beside Activities. Users have a choice of allowing each Activity to have its own virtual desktop, or of setting virtual desktops so that each can have its own collection of icons and widget and ignoring Activities altogether.
KDE includes Desktop Effects that require 3-D hardware acceleration. However, many effects do not, nor does KDE itself.
At a time when 3-D support is still spotty, especially if you only use free-licensed software, this practice gives KDE a major advantage over other desktops, allowing it to be used without workarounds and/or a major reduction in responsiveness. Which raises the still unanswered question: Why should two-dimensional desktops require three-dimensional support in the first place?
Average users may rarely notice, but the KDE 4 release series began as modular, and has become more so with every release.
This modularity has not always been successful. In particular, Akonadi, the personal information manager, has been buggy over many releases, and offers few hints of how to repair it.
However, in other modules such as Plasma, modularity has allowed KDE to plan for different form factors, redesigning interfaces for notebooks and tablets without doing major redesigns of the rest of the desktop.
As a bonus, even when an interface is no longer needed, such as the Plasma Netbook, it can be retired as a template for Activities. At its best, modularity makes KDE easier to adapt to evolving demands and user cases, and to waste as little as possible.
Once the basic feature set was added to the KDE 4 release series, the project began to regularly update the code -- so much so that some of the recent releases have been more about revision than new features. In fact, the KDE 4.12 release was plainly announced as being for applications rather than for the desktop itself.
Such an emphasis on updating can be disappointing to users. However, it promises to make KDE more adaptable. It should also avoid crises like the one approaching for MATE, which will soon have to upgrade from the GTK2 toolkit if it is to continue supporting GNOME applications.
Both GNOME and Unity are designed to limit clutter -- that is, icons on the desktop and applets on the panel.
The only trouble is, this so-called clutter is a major source of customization. Instead of eliminating or reducing this clutter, KDE has encouraged it. Folder View widgets give users the option of maintaining multiple icon collections on the same desktop, or of swapping them in and out as needed. Similarly, widgets place even more on the desktop. Far from reducing clutter, KDE has increased it -- a move that users seem to rank highly.