A more realistic approach for a cross-platform WPF might be to start with Mono's Moonlight (as Silverlight and WPF have a lot in common) - this could now be speed up by using parts of WPF.
However in 10 years no one has cared enough to start a project to do this, so I'm not too optimistic.
Couldn't this be a good competitor for Electron or React native? Write code in whatever language you want that compiles to .Net, make the UI in XAML, don't run the application on Chrome and Node. Sounds like a good candidate for cross platform development.
However in 10 years no one has cared enough to start a project to do this, so I'm not too optimistic.