. . . upgrading to Windows 10 thinking they'll always have the Windows 10 Upgrade for Assistive Technology Users offer, this just in from user Timothy (he doesn't use a last name on the mailing list) regarding that offer:
In July 2016, we shared the offer to extend the free Windows 10 upgrade. This extended availability is now coming to a close, as we’ll wrap this offer at the end of 2017.
Note that the Windows 10 upgrade for assistive technology users' page has yet to reflect this date, but I'm sure it will in due time.