Unnamed sources recently informed The Verge that Microsoft plans to reveal Windows 9 "Threshold" at a special press event on September 30. These sources indicated that Microsoft will release a technical preview of the upcoming OS to developers on that date, or shortly thereafter. The sources did not mention the rumored customer preview.
According to the report, the technical preview will include the new Start Menu, which will have both standard links and animated Start Screen tiles. The preview will also see the removal of the Charms bar on the desktop, and possibly an early version of Cortana, which in recently leaked builds materialized as a Start Screen app.
News of the technical preview surfaced last week, reporting that the Windows 9 end user will be required to accept automatic monthly updates if they choose to install the preview build. Rumors also indicated that the technical preview would be open to the public. However, Microsoft customers will likely be encouraged to wait for a consumer preview that may or may not launch in December or early 2015.
In addition to the new Start Menu and the removal of the desktop Charms bar, Windows 9 "Threshold" is also expected to introduce floating, resizable, windowed Modern UI apps on the desktop. Windows 9 will also boot directly into the desktop if the customer doesn't have a touch screen, or boot into the Start Screen if a touch screen is detected. Based on leaked builds, Windows 9 "Threshold" will also provide virtual desktops.
So far, rumors claim that Windows 9 may not cost a dime for customers upgrading from Windows XP, Windows Vista, Windows 7 and Windows 8/8.1. That sounds a bit far-fetched, but it could make sense for Microsoft to release the rumored "barebones" version for free (Windows with Bing?), and a premium version that can be bought outright or consumed as a monthly subscription, similar to what Microsoft does with Office 2013.
Currently, Windows 9 "Threshold" is expected to go retail in Q2 or Q3 2015. Rumors have pointed to Spring 2015, but that could change if Microsoft runs into a snafu caused by developer and consumer feedback. Still, all the rumors and reports seem to point to a familiar pattern that Microsoft followed with the original Windows 8 platform: The developer preview (Sept. 2011), the consumer preview (Feb. 2012), and the RTM version (Aug. 2012).
Using that timeline, Windows 9 may not see a consumer preview until March 2015, and the RTM somewhere around July or August 2015, which fits into previous rumors that the updated OS may not launch until Q2 or Q3 2015.