For the majority of users, the Windows 10 free upgrade period has just ended. That said, Microsoft is extending the offer for a specific group of people: those who use assistive technologies, such as text-to-speech software for those with visual impairments. They are being intentionally vague with which AT software allow users to qualify, which makes sense, because being pedantic to users with disabilities after offering it to everyone (sometimes like a hot potato) for a whole year wouldn't be the best PR.
They haven't yet announced an end date for this new offer. They also haven't really discussed why they are making this exemption, although they do promote the upcoming Anniversary Update several times, with its new accessibility features highlighted. This makes me think that, while of course Microsoft is going to namedrop the new build whenever possible, they might have found that users were hesitant to upgrade to 1507 and 1511 because of accessibility concerns. Since the general public upgrade offer ended just before the Anniversary Update, they might be allowing those users to jump aboard Windows 10 even though their disability prevented them from using 1511.
Either way, it's a nice extension to make.