A April 4 blog post on the Silverlight Team Blog, signed by Scott Guthrie, Walid Abu-Habdha and Soma Somasegar, revealed that Microsoft will be making a beta of Silverlight 5 available the week of April 11, concurrent with the Mix '11 conference.
The final version of Silverlight 5 is due before the end of calendar 2011.
The blog post also notes that Microsoft plans to share more about its HTML5 tooling strategy in the near-term:
While we've emphasized the role of HTML5 as the foundation of the recently released Internet Explorer 9 and have shown an unprecedented commitment to being leaders in HTML5 browsers, we've probably not emphasized enough the tooling for HTML5. We're going to emphasize that much more going forward as the clarity of feedback and the emphasis our customers want us to place on these tools for the professional toolbox is clear. It would be fair to say to the degree we didn't emphasize the above we made up for it in our emphasis in Silverlight as a runtime (and by extension XAML).
The authors of the blog post also said that Microsoft isn't favoring one technology over another and that there's room for both. Because the authors are affiliated with Microsoft's Developer Division (the Silverlight champions), not Windows Client (the HTML5 champions), the understandable emphasis in the post is on the future of "plug ins" (i.e., Silverlight as a browser plug-in).
"Today, plug-ins and standards play complementary roles, and as a practical matter there is no single technology to satisfy all the needs demanded by client development. While much has been written about a diminishing gap between the capabilities of HTML5 and capabilities provided by plug-ins, plug-ins will continue to evolve and so there'll likely be a gap of some degree, and it'll cyclically contract and expand. Contraction occurs as the standard specification "catches up" with the plug-in technologies, and then expands again as the next wave of innovation pushes the boundary further forward."
[Source: Silverlight Team blog]