Like C# and ASP.NET, Silverlight should allow you to use the MailMessage and SmtpClient classes without having to reference a web service. It should also have a built-in POP/IMAP class.

<#Region This is Test Region>
<My Xaml code goes here>
<#EndRegion>

This should provide me collapsible regions within xaml that should be similar to what exists in C# like #region -- #endregion

Remove sealed from Image, TextBlock and PasswordBox classes so that we can derive these controls to add extra functionality or for styling purposes.

This was marked "completed" for Silverlight 4 but the original request is for "full" keyboard support. There are too many use cases to list here. There are a large number of requests in the forums -- the Silverlight 4 approach gets us closer. Many applications which benefit from full-screen support require keyboard input. One possible solution is to display an "opt-in" message requesting the user's permission to allow keyboard input to be collected.

Error handling in Silverlight has been a major problem since it started. It does not have a proper error reporting technique and most of the time ends up with issues like AG_E_UNKNOWN Exceptions and XamlParseExceptions with StackTrace and Data as null most of the times. Proper error messages need to be given and if possible will be better to highlight parser errors while compiling

It feels ugly to know we still cannot run beautiful silverlight applications in Android, iphone etc etc.

That limits use to think while using silverlight for developing data driven application.

Need for the same model as WPF provide:
- CoerceValueCallback,
- DependencyProperty.RegisterReadOnly

Adding Binding expressions to templates adds a significant overhead to render time of elements. Ie. binding width, height and color on an ellipse DOUBLES the time it takes for the element to appear on screen.

Just the runtime should be able to understand a .xap and no humans can rename it to zip and take everything inside it and also recompile dlls in it so making the xamp completely unreadable by a human would be the most important one.

This is a bug. Please fix it. https://connect.microsoft.com/VisualStudio/feedback/details/715768/closing-silverlight-childwindow-does-not-reenable-rootvisual

Making easier and Designer friendly the handling of themes and enabling them as separate libraries style "Metro.theme.dll" which we can easily relate to a project and switch them dynamically.

For Out of Browser Applications, it would be really helpful if one could register a custom file extension with the OS so that opening a file would automatically launch my Silverlight OOB application. Adobe AIR has the ability.

AppleScript support on Mac OS X

PLEASE MAKE A SILVERLIGHT APK SO I CAN WATCH HULU AND SILVERLIGHT VIDEOS ON MY PHONE PEACE

Implement/port the required framework code to support xsl transformations on the client.

Add support for OOB Silverlight applications to identify and use multiple monitors.