AppleVis shares a detailed article about the new and changed accessibility features in iOS 10. The article covers:
Mainstream Stuff Impacting Accessibility:
SiriKit, automatic image descriptions, Home to Unlock, VoiceMail Transcription and Raise to Wake
Moving apps rotor command, Customize VoiceOver pronunciation, new VoiceOver voices, VoiceOver Settings - expanded and reorganized, added VoiceOver sound hints, and Mail app display changes
Braille command for 3D touch, spoken feedback for contracted braille, and Braille readers can now access name of wireless network
Choose words, sentences or both for Speak Selection, Typing Feedback (without VoiceOver), and changes in Setting categories
New set of features for TTY users!
Note: This article was dated on Sept. 13, 2016 just prior to the iOS 10 release; it does not cover known bugs or issues.
UPDATE: After iOS 10 was publicly released!