The Winter 17 Salesforce release included a new format for Extended Metadata (XMD), which is used to customize the formatting of dashboard elements in Wave Analytics. The pre-Winter 17 version is known as XMD 1.1, while the new format is XMD 2.0.
In addition to the format change, XMD became a Base Platform Object, rather than a JSON file on the dataset. You still use JSON to specify and upload the XMD. As a Base Platform Object, you can manipulate JSON through APIs, such as the REST API through workbench. It also means the XMD format and contents are validated, allowing only correct JSON files to be uploaded.
While there is an XMD Overview and Reference guide in the developer documentation, some of the examples still retained the 1.1 format. There is also a help document that discusses the transition from 1.1 to 2.0, which give before and after pseudo code.
What I did not find were before (1.1) and after (2.0) examples for transforming each section of an existing XMD 1.1 file. Here is my outline for turning XMD 1.1 into XMD 2.0, section by section, with before and after examples.