So it's crappy HTML and JS underneath? I was hoping for cross-platform WPF :(.
I think a better foundation for a cross-platform editor/IDE would be SWT, the Standard Widget Toolkit from Eclipse, perhaps ported to .NET.
For decades of trying, this is the best we've managed to do for cross-platform UIs. It ain't great, but it soundly beats the alternatives.
WPF also abstracts control behavior away from presentation and allows you to easily and quickly extend the base set of controls to do whatever you want to.
After building multiple thick client applications using VB6, MFC, Swign, Winforms and WPF, WPF exceeds all of these, by far, in flexibility and maintainability.
For me, the real value is composition flexibility.