Although the free upgrade period for Windows 10 is over (it ended July 29th 2016), users that require assistive technology still can upgrade their OS to Windows 10 for free. If you have any assistive technology in use, you can benefit from the offer. Microsoft does not restrict to any particular assistive technology, and the upgrade offer period currently has no ending date.
The reason for the extended offer is that there are still numerous AT devices out there that are still not supported on Windows 10. Microsoft extends the offer so that manufacturers have more time making their devices compatible with Windows 10, allowing the end user to still benefit from the free upgrade to Windows 10.