I could not open the workbook. Instead, I received a message that it was created in a newer version of Tableau, which is odd since I am on 10.5.2. The XML file said it was version 18.1. ???
The Extensions API is in a developer preview right now, you can talk with your Tableau sales rep to get access and then you'd go to http://prerelease.tableau.com to get the preview.
Also working with the Extensions API is covered under NDA at this time per the prerelease site so I'm assuming that since @Aania is a Tableau employee that she has permissions to talk about it.
Oops I got a little too excited and posted this early! This will be accessible on April 30 (when 18.2 is in beta).
Promise it’s worth the wait!
It did sound pretty cool. I’m looking forward to the reveal.