At the Build Developer Conference earlier this year, Microsoft officially announced plans to return the Start menu to “the next iteration of Windows,” along with a new option to run Metro/Modern-style apps in their own windows on the Windows desktop.
Microsoft Executive Vice President Terry Myerson made the announcement at the Build Day 1 keynote on April 2, 2014. You can watch the clip on YouTube, with Myerson's remarks coming a little more than two hours in
to the morning’s proceedings.
This screenshot is taken from the demo (prerecorded, not live) that played on the screen behind him:
And this week rumor sites are abuzz over the appearance of a newer version of that Start menu, as seen in a screenshot supposedly taken
from a recent (leaked) build of Windows. It could appear as early as this fall.