Silverlight 5, the most recent -- and possibly last -- version of Microsoft's cross-platform browser plug-in, is poised to be released to manufacturing (RTM) before the end of November.

Several of my customer and partner contacts have told me they have heard from their own Microsoft sources over the past couple of weeks that Silverlight 5 is the last version of Silverlight that Microsoft will release. They said they are unsure whether there will be any service packs for it, and they are also not clear on how long Silverlight 5 will be supported by Microsoft.

(There's no end date yet on Microsoft's lifecycle page for free support for Silverlight for Silverlight 4. According to the page, Microsoft must give developers and customers a year heads-up before ending support for any given Silverlight version. Free support for Silverlight 3 ended in April 2011.)

One of my contacts said he believed that the final version of Silverlight 5 may only work with Internet Explorer on Windows and won't work on Mac OS platforms or with other browsers at all. (Silverlight 4 supports Windows and Mac OS X and the IE, Chrome and Safari browsers.)

Yes, I know -- everyone's been rushing to proclaim Silverlight dead for more than a year now. In fact, I'm frequently cited as the source of that prognostication, in spite of the fact that all I've actually reported is that Microsoft's strategy with Silverlight shifted and that Silverlight is no longer Microsoft's cross-platform runtime solution. Instead, Microsoft currently positions Silverlight as a tool for creating rich media, line-of-business and smartphone apps. When I wrote about Microsoft's morphing Silverlight strategy back in the fall of 2010, I noted that company officials only committed to one more release after Silverlight 4 and said nothing more about the Silverlight platform's longer-term future.

Microsoft officials are remaining mum about whether there will be any more Silverlight releases after version 5. I asked again on November 8 to see if the Softies would say anything at all regarding the company's post-Silverlight 5 plans and was told by a spokesperson that the company had "nothing to share at this time regarding exact timing, future releases or support."

There is some anecdotal evidence suggesting Silverlight 5 may be the end of the road -- beyond the continued reassignments and/or defections of many at Microsoft formerly working on Silverlight and the major reorg affecting the Silverlight team earlier this year.

Here's what we know. In an October 26 Webcast with the Linked.Net user group, Scott Guthrie said that Silverlight 5 would ship "next month," meaning November. (I'm hearing the actual RTM date could be this week, in fact.)

Guthrie also said during the same Webcast that Microsoft was close to shipping Silverlight on "other devices" (meaning the Xbox 360, I'm assuming). In his responses to Webcast participants' questions about the future of Silverlight, Guthrie didn't mention anything about Silverlight being continued beyond Silverlight 5 or provide any indication there would be anything coming beyond Silverlight 5.

As many will be quick to note, Guthrie's decision not to talk about the future beyond Silverlight 5 may simply be due to Microsoft's increasing information lockdown on futures and roadmaps. It's also worth noting that Guthrie is, as of earlier this year, focusing on Windows Azure app development and not leading the Silverlight team.

Those caveats aside, I found Guthrie's choice of wording on the Webcast interesting. He talked about Microsoft's mission in making XAML "a first class citizen" and differentiating from its competitors using XAML. He emphasized that Microsoft is neither moving away from XAML nor discontinuing its support of XAML. He didn't say the same of Silverlight.

Is the distinction a big deal? I mean, do developers really care whether Microsoft continues to crank out new Silverlight releases, as long as those who want to use Silverlight to develop for Windows Phone, Windows 8 and Xbox can use their XAML skills to develop for those platforms for (some unknown number of) years to come?

One tech consultant with roots in the Microsoft world said the XAML/Silverlight lines are blurring.

“It’s pretty clear to me that the principles of Silverlight, including the use of XAML as a markup language, C# and VB .NET as programming languages, a streamlined .NET CLR (Common Language Runtime) profile, packaged deployment over HTTP and a sandboxed security environment, are alive and well in the native XAML/.NET approach to developing Metro-style apps on Windows 8. It may not be not Silverlight to the letter, but it’s Silverlight in spirit and natively supported by the operating system to boot," said Andrew Brust, a Microsoft Regional Director and founder of Blue Badge Insights.

(Brust noted, for the record, he hasn't heard whether Silverlight 5 is the last version of Silverlight or not.)

If Silverlight 5 is the end of the line for Silverlight, do you care? Why or why not?

Update: Looks like Microsoft isn't the only one wrestling with what to do with its rich media plug-in and runtime. As unearthed yesterday by my ZDNet blogging colleague Jason Perlow, Adobe announced on November 9 that it is discontinuing work on the mobile version of Flash and is instead focusing on HTML5. Adobe is continuing to develop new Flash releases but is focusing that work for PCs and mobile apps. It would be great to see Microsoft issue a similar, comprehensive statement about its future intentions with Silverlight....