Microsoft has already softened their pricing strategy by offering Windows for free on small tablets and by not charging for the upgrades from Windows 8 to 8.1 or to 10.
Perhaps they don't see Windows as the cash cow that it once was and will make all upgrades free.
This is because 8 and 8.1 are a downgrade compared to 7 and weren't received well. Consider that Windows XP has a bigger market share than 8 and 8.1 combined.
It wouldn't surprise me to see them make the base OS for home users free, and then only charge for enterprise specific features. Think of 7 Home Premium as free, and Ultimate/Enterprise now the paid versions.
Perhaps they don't see Windows as the cash cow that it once was and will make all upgrades free.