While I wouldn't call this an official MS communication it sounds promising:
"Gabe Aul, an engineering general manager for Microsoft’s operating systems group,
said in a tweet that people who upgrade a device to Windows 10 during the first year of its existence will be able to perform a clean reinstall of Windows 10 on the same device “any time.” It’s good news for upgraders who are concerned about what will happen to their devices a year after its July 29 launch.
Also, people won’t need to hold onto their Windows 7 or Windows 8.1 product key in order to perform the restoration. Their devices will reactivate themselves after being upgraded to Windows 10,
Aul said."
Windows 10 upgrade will allow clean installs on the same device for free | PCWorld