The next version of Windows, codenamed "Threshold," is going to include some fairly major user interface changes beyond the inclusion of the new Start menu and "Modern" app windowing.
A couple of reports from earlier this week cited some other interface changes coming to Threshold. My sources are corroborating those reports.
First up, as reported by Brad Sams at Neowin.net, Microsoft is moving toward adding virtual desktops to Threshold, the Windows release expected in the spring of 2015. As Sams noted, other operating systems, including Apple's OS X and Ubuntu, already support virtual desktops, which allow users to run and switch more easily between apps and groups of apps.
The other UI change coming to Threshold is the elimination of the Charms Bar, as first reported by Winbeta.org.