It seems to be inevitable that this will be a demand placed upon me and my team (though I sure plan to explore Xamarin.Forms or some other smart client cross-platform solution if one takes shape). I will have to move our very large Silverlight application to HTML/JS.
That was also my concern some years ago, The quest for an alternative led me to http://www.visualwebgui.com/. Visual WebGUI keeps improving and now it's free (as in bear).
I don't know if you met VisualWebGUI before, but you take a Windows Forms application and you can migrate it to VWG with minimal changes, PROVIDED you don't use third party controls.
CslaContrib supprts VisualWebGUI by implementing the Csla.Windows control library (as CslaContrib.WebGUI).
For those who used to know VWG, the most annoying non-feature was the asynchronous modal dialog forms. Now all modal dialog forms are synchronous and that makes easier the migration from WinForms to WebGUI.
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