Add support for custom data connectors (Power Query M extensions)
Custom Data Connectors mechanism is being developed by Power BI Desktop team:
Excel's Get & Transform engine (Power Query) should have support for *.mez/*.pqx extensions too.
Vitaly Potyarkin commented
Custom connectors have reached "General Availability" status in PowerBI: https://powerbi.microsoft.com/en-us/blog/announcing-general-availability-of-custom-and-certified-connectors-for-power-bi/