I'm also assuming that this is what business is intending to do with new Win8-Pro desktop/laptop purchases - same as they did with Vista purchases downgraded to WinXP.
However, MS have done plenty of inexplicable things in the past, so anything is possible.
The difference with businesses is that they buy Software Assurance which 1) keeps them licensed for the then-current version of Windows and 2) always gives them downgrade rights to whatever version they need to run in their enterprise (which is how Microsoft was able to say businesses were flocking to Vista/7 even though they were still on XP).
If non-business XP to Win8 upgraders without SA get downgrade rights to Win7, it will be the first time Microsoft has ever allowed that.
But hey --- you don't need to run Metro and the desktop is still there. Why would you need Windows 7 if you upgraded to 8? It's not like anyone's being forced to use the Metro start screen or Metro apps. At least, that's what I keep hearing here.