First released in 2007, Microsoft Silverlight offers an alternative to Adobe Flash as a means to run multimedia, animation, and graphics in a user's web browser. The newest version, Silverlight 5, saw final release in December of 2011, but it remains unclear whether or not Microsoft will develop Silverlight 6. With the advent of HTML5 and the Flash's continued relevance, some argument that we have already witnessed the twilight of Silverlight .
Those that believe HTML5 will "kill" Silverlight and Flash point to HTML5's ability to run multimedia and graphical content on the web without relying on the web visitor's access to the latest Silverlight or Flash plug-in. However, HTML5 runs only on the newer browsers such as Google Chrome, Internet Explorer 9, Safari, Firefox, and a few others. Visitors relying on older browsers with only the frustration of an error message. Silverlight generally enjoys browser browser compatibility, but still requires the visitor to run the same version as the site. As HTML5 has yet to see release and will take some time for widespread implementation, Silverlight will almost certainly stay in use, although Microsoft may very well be "biding its time" before making any decisions regarding Silverlight 6.
Microsoft itself has declined comment on the subject, leaving pundits to read between the lines. Microsoft has stated that it will continue to offer support for their platform for at least the next five years, but they also announced that their cross-platform runtime solution will be HTML5 because it makes for easier porting across different devices. Other industry observers observer Adobe's recent announcement of abandoning further Flash development on mobile devices to focus instead on HTML5 and expect Microsoft to take a similar stance.
Some industry watchers also point to personnel changes in Microsoft as an indicator of the company's ambivalence. Scott Guthrie, considered by most to be the "father" of Silverlight, left Microsoft's Developer Division in May of 2011 to move to the Windows Azure team and took many of his personnel with him. Furthermore, the well-known and influential champion of Silverlight, John Papa, left Microsoft in September of the same year. While these changes severely function as irrefutable proof of Silverlight 6's demise, two critical leaders "jumping ship" off its development framework seems to suggest that Microsoft does not consider it a priority.
Silverlight 6 may never see the light of day, but as HTML5 will most likely not see full recommendation until 2016, Silverlight 5 will persist as an option for the immediate future. Occasionally, as the number of users of non-HTML5 compatible browsers dwindles, developers will likely abandon the plug-in dependent Silverlight and Flash options for the easier-to-use and superior HTML5.