Many noted that knowing there is a group of windows just by glancing at the task bar is important to them. Very, very few find value in the little number, however. So putting it all together, in 4.10 a small arrow will be shown drawn over the window icon when there is a group, as is seen in many other dock apps. This preserves the most useful information while also limiting visual noise, creating a more compact layout in the window listing and finding consistency with other implementations out there in the wild.
As a bonus, the arrow is no longer the (in my opinion) ugly black thing that was specific to the window list but the standard arrow used throughout the rest of the Plasma workspace interface.
Thanks to everyone for your feedback!
Bonus time! ;) A curious little walk down memory lane: in the later 3.x releases of kicker (I forget if it was 3.4 or not; but around that time, I believe) I implemented a new look for the tasks widget which was made configurable via the task applet's configuration dialog. The old look was kept as "classic" and the new look was named "elegant". When Plasma Desktop 4.0 was released, the tasks widget was rather different and looked a lot more like the "classic" style, but I kept to my commitment of deferring these things to the people doing the graphics, as long as they did not impact usability (which would trigger a discussion to find a consensus-base solution). With 4.10 we are now back to something much like the default "elegant" layout in later 3.x tasks applets. The grouping element is now nicer, but otherwise .. it's "elegant" from the old days. It's funny how sometimes things go full cycle like that. I'm just enjoying my nice, calm panel with fewer lines and borders.
|Current master, which will eventually be released with Plasma Desktop 4.10|