Windows 10 is likely to cross over to "Insider Preview" branding from today for all those enrolled in the Windows Insider Program. This can be backed up by the "accidental" leak of almost
all language variants of build 10074 yesterday, directly from Microsoft's servers, which are branded as such.
Now, famed Windows leaker WZor has tweeted that all Insiders will be upgraded to the RTM version, regardless of the base install. It's well known that many Insiders have clean installed Windows 10, therefore not coming off a valid license for the upgrade path of Windows 7 and up.