This looks very much like the REST API that MS released back in 2011 for the SharePoint hosted Excel Services [1]. Obviously that configuration required a SharePoint deployment on your own server. It looks like this new offering [2] [3] simply makes that functionality available on the MS Cloud for .xls[x] that are stored on OneDrive. IIRC the 2011 SharePoint Excel Services didn't support VBA or addins which are often critical for the heaviest spreadsheets that are most in need of serverization. I can't find any mention of addins or VBA in the docs for this new REST API, so I'm guessing those aren't supported.<p>[1] <a href="https://msdn.microsoft.com/en-us/library/office/ee556413.aspx" rel="nofollow">https://msdn.microsoft.com/en-us/library/office/ee556413.asp...</a>
[2] <a href="https://blogs.office.com/2016/08/03/announcing-the-general-availability-of-the-microsoft-excel-api-to-expand-the-power-of-office-365/" rel="nofollow">https://blogs.office.com/2016/08/03/announcing-the-general-a...</a>
[3] <a href="https://graph.microsoft.io/en-us/docs/api-reference/v1.0/resources/excel" rel="nofollow">https://graph.microsoft.io/en-us/docs/api-reference/v1.0/res...</a>