Hi,
I have found it is not possible to connect PowerApps to Excel Sheets stored in SharePoint Document Librarys., I guess I am not alone in having Excel Sheets stored in this way - and wanting to add a mobile layer to allow end users to update more easily.
As Power apps already supports Excel Sheets stored in One Drive for Business and access to SharePont lists, I would guess (with no knowledge!) that this would be easy to add?