Power BI Datamart vs Power BI Dataset vs Azure Analysis Services

I'm looking at the new Power BI data mart functionality that has just been released. Best I can tell it gives the same result as creating a dataset in Power BI desktop except it's aimed at non-developers and your stuck in a browser so loose all control over any source control / file versioning.

One things that does stand out is the XMLA endpoint for read users from Excel. This is somthing the datasets have desperately needed for some time. Currently you can connect but you need contribtor permissions to the workspace in order to be able to "read" the data from a dataset through Excel. This makes a huge security gap when it should be read only users.

A lot of businesses still have the need for cubes and being able to slice and dice the data through Excel as well as report it. Recreating the same data model in analysis services and Power BI is redundant. Is there any where on the roadmap where we can create a datamart using an existing dataset created in Power BI desktop?, this would be to effectivly make use of the read endpoint over existing datasets. Or alternativly is there any plans to fix the viewer role in regards to datasets and the XMLA endpoint.