WPF has only been tweaked a little here and there since around 2010 or 2012. Then they started pushing Silverlight and WinRT. I remember distinctly the moment around 2012 when we realized that WPF is pretty much dead in the sense that nothing new will be coming..
I'm aware it was used in Visual Studio, and oh, the Expression Studio suite [0] – another discontinued line of great products, for making stuff with WPF – but that's all I can remember.
Not even Calculator or Notepad used WPF as far as I know, which would have been the simplest apps to port and could have bolstered developer confidence in the technology (the point of this whole discussion.)
Correction: Apparently most parts of Expression Studio have been assimilated into Visual Studio, but the point remains: It decreased developer confidence when it was discontinued and nothing was immediately announced as a replacement.
It was barely dogfooded at all by Microsoft themselves and the future we got instead was the bland, inferior “Metro” experience.