Microsoft's GUI problem is two-fold.

Firstly, that nobody believes them when they swear that {new GUI framework} will be the future and used for everything. Really. Because this time is not like those other times.

Secondly, pre-release user feedback. Ironic, given other parts of Microsoft do feedback well.

Imho, the only way MS is going to truly displace WinForms at this point is to launch a 5-year project, developed in the open, and guided in part by their community instead of internally.

And toss a sweetener in, like free app signing or something.