According to Paul Thurrott, Microsoft won't release the .iso to the general pubic.
1) releasing an "official" retail, full 8.1 iso for 8.0 upgraders (like the Technet/MSDN iso's that do not support full upgrades from Win7 but only from 8.0)
Quote: Paul T:
Microsoft told me that is not happening.
Kinda sucks for those who don't have access to a subscription.