Chris Green , a product manager at Microsoft,has published a roadmap,estimating the Product Support Life Cycles for various product. He has not just published the life cycle of various released products but have even mentioned about the Windows8,Windows Server 2012 and several other upcoming products.
Some important dates which was published in the roadmap are
- Support normal: 1st July 2011 to 1st July 2016
- Extended Support: 1 July 2016 to 1 July 2021
Windows Server 2012
- Support normal: July 2, 2012 to June 30, 2017
- Extended support: July 3, 2017 to 1 July 2022
So,if going by these dates,the RTM version of Windows 8 would be available by July 2011. Windows 8 being a major release, a radical change is expected and it seems bit impossible that Windows 8 would be RTMed by July 2011.
Chris has clearly posted below the pdf file that This information is provided as a guide only and is likely to contain errors so we may hope some changes in the roadmap.
Download the Roadmap Here