Now that we have an idea when the update will be taking place, it might mean that those hoping to see the next high end Windows Phone model from Nokia will have to wait until the holiday season. Just the other day, we passed along to you the word from Greg Sullivan that Windows Phone 8 does have "an upgrade path going forward." Unlike Windows Phone 7, which had a rather rigid set of hardware requirements, Windows Phone 8 is more flexible. Sullivan also added that the Redmond based company is following a new policy which he calls a "shut up and ship" philosophy where the company doesn't release information about a product well in advance of its launch.
source: MicrosoftCareers via WMPoweruser