Win8 pro will have the Virtual machine option along with Win8 enterprise, Win8 Enterprise will not be available to retail though as it is for companies / corporations with volume license agreements.
You cant upgrade from win8 to win7 pro Microsoft will class that as a downgrade.
Microsoft will be allowing manufacturers of pc's to offer a downgrade from win8 to win7 with new pc's and laptops very similar to what was offered when Vista first became available.
Have you actually tried Win8 yet? if not i seriously suggest that you download the 90 trial of Win8 from Microsoft and either run it as virtual machine in Win7 or do a dual boot to try it. Please not that the 90 trial version Microsoft has made available is actually Win8 enterprise that won't be available to retail (enterprise ahs a few things in it that aren't available in other versions. You also can not convert the trail to a full version by purchasing a product key. It will stop running after 90 days.
A few links worth looking at. http://www.eightforums.com/ http://www.windows8update.com/ http://www.winsupersite.com/ http://windows.microsoft.com/en-US/windows-8/release-preview http://msdn.microsoft.com/en-us/evalcenter/jj554510.aspx http://www.zdnet.com/blog/microsoft/microsoft-details-its-windows-8-upgrade-plans/13051