I represent a small company with 4 paid apps on the Amazon App Store.
Thanks to the open source (MIT) set of tools called fastlane (http://fastlane.tools) (now part of Twitter Fabric), we now have automated deployment for binaries and metadata for iTunes and Google Play. Amazon App Store is missing, and the Developer Publishing API would help. Regarding fasltane, we are tracking this issue here: https://github.com/fastlane/fastlane/issues/1963
I tried to get in touch with Amazon a few times through different channels in the past months just to discover this Early Access API yesterday. I registered to the beta but I am not sure if I will be accepted given our developer profile.
I would love if someone at Amazon could take contact to discuss your plans further regarding this API, here or on a conf call.