Sources say that Microsoft is targeting March 11 for the release of Windows 8.1 GDR1. That falls on Patch Tuesday, meaning the update will be distributed through Windows Update. There's also talk that this update will be rather minor.
The same sources informed ZDNet that GDR1, or Update 1, will focus on reducing Windows 8.1's footprint both on the drive and in memory. This move is expected to allow the platform to run on cheaper, small tablets.
As previously reported, Windows 8.1 GDR1 may allow users to pin Metro-style (Windows Store) apps to the desktop's taskbar. Thumbnail previews will also be rendered on the desktop when a mouse cursor is placed over the taskbar icons. "Close" boxes are even expected to be added to the Metro apps.
If Microsoft does choose to launch GDR1 on March 11, that would be before Windows Phone 8.1 "Blue" arrives. Sources claim that the updated phone platform won't go RTM until just before the kickoff of Microsoft's BUILD convention, which starts April 2. Customers won't have access to Windows Phone 8.1 until the end of April at the earliest.
Given that Windows Phone 8.1 and Windows 8.1 GDR1 will be released around the same time, there's currently no indication that new APIs will be available to bring the two platforms together. Instead, GDR1 will focus on making Windows 8.1 more useful in the business/enterprise sector.
There's also currently no sign of the "mini" Start Menu. This is expected to arrive in a possible GDR2 update in the fall (the first rumored Windows 9 window), or in Spring 2015 during the "Threshold" wave that includes Windows Phone 8.2 and the major Xbox One update.
As always, this is pure rumor and speculation. Perhaps we'll hear more about GDR1 within the next couple of weeks.