Fast forward 9 years after the question, and you kinda have it, on Windows 10.
It won't work exactly as you asked, and it will not work for all of your windows, but it may help you, if you adjust your workflow.
If you hit
Windows logo key + number, it will activate the application that is located at that number in your taskbar. For example, if Windows Explorer is the first icon in your task bar, hitting
Windows logo key + 1 will activate it.
Now, you may have several windows stacked on that icon; keep the
Windows logo key down and keep hitting
1; it will cycle through the list, till you hit the one you want.
That might be the blinking one, or any. It is a real time saver for me.
To make the most use of it, pin the applications you use the most on the task bar at the first positions, so their number is always the same. It's very efficient for me to use that technique on the first four apps in the task bar. Unfortunately, the numpad does not work for that.
It doesn't work for all of your windows, because it accepts only single digits (so, 10 apps).
Super + Number also works, for the items on the docker. Not sure about KDE.
For windows past the 10th position, you can use
Windows logo key + T; it will allow you to navigate on the task bar with the arrow keys. Not very efficient, though.