Microsoft's Gabe Aul has confirmed the news on Twitter:

Any PC that is upgraded from Windows 7 or Windows 8.1 to Windows 10 will lose the Media Center functionality, and there's no way to get it back. The decision is a disappointment to the small but incredibly vocal army of Media Center enthusiasts, who had held out hope that a Windows 10 Media Center add-on, similar to the one offered for Windows 8, might appear at the last minute. In a private meeting this week at the Build developers' conference in San Francisco, a Microsoft executive confirmed to me that there will be no update to the company's Media Center software for Windows 10.