Couchbase, a NoSQL database provider, has published a write-up on how to use Power BI with their Couchbase Server. It is a great outline of how Power BI can work with just about anything that has data. You can find it here: PowerBI & Couchbase Server 4 - Reporting over JSON Data with native connectivity.
And, on the SQL Server Team Blog:
JSON in SQL Server 2016: Part 1 of 4, On the teams blog are four posts cover JSON.