Microsoft has not yet specified a release date for Windows Phone 8. Hardware partners like Nokia already showed their Windows Phone 8 devices, but the OS is not ready.
Nokia unveiled this week the Lumia 920 and Lumia 820 Windows Phone 8 devices and they look very promising. The event lacked pricing and release dates. According to Arstechnica the reason for this is that Windows Phone 8 is not ready.
At the Nokia event the phones have not been available for the press to play around. Windows Phone developers still do not have a developer SDK for WP8. Rumors saw the release of the Windows Phone 8 devices at the end of October. This seems under this circumstances not likely.
The worst thing that can happen is that Microsoft needs to delay the Windows Phone 8 launch to 2013. It would take away the boost that phone sales get during the crucial Holiday shopping season.
The reasons for the delay are likely the change to the NT Kernel and APIs.