2 features that really interested me were the X-Ray and the Audible integration, where you can buy the Kindle book and pay an additional, reduced fee to get the Audible version. You can listen to the Audible version on iPhones, Androids or Kindle Fires, but then you can pick up and read the text from a Kindle eInk device, or Kindle Fire.
I'm basically asking, are older Kindle devices getting updated firmware to introduce these features or are they pulling an Apple where you can only have them if you buy the newer device. Note the link below indicates "read with any eInk Kindle device".
https://www.amazon.com/gp/feature.html?docId=1000827761