Hi, I'm not really a master guru at using c#/html5 but , in the roadmap there is not mention about visual basic. If your aplication is made with silverlight and VB as code behind then at least the xaml files can be reused with some minor change, but for the VB code, perhaps there is some kind of tools to convert to c#, I found this one a good start http://converter.telerik.com
In theory is the IL that is compiled to JS not C# so any .NET language should work not only C# but VB, F# and so on... Probably the only that will never work is C++/CLI but that is satanic