Agreed on the crappiness of the web stack for this application. But WPF isn't necessarily better. Case in point: a Bible study program where one's choice of video card actually mattered, at least in 2009 (see http://community.logos.com/forums/t/6200.aspx). BTW, I only know about that specific example because my brother is a preacher.

I think a better foundation for a cross-platform editor/IDE would be SWT, the Standard Widget Toolkit from Eclipse, perhaps ported to .NET.