Very long time since I even look at Access.. but on SPO, with a database on Azure it seems really nice ... wondering tho..
1. Any way to remove that left pane with the Databases from the UI?
2. Set a list button to go to a URL formatted using selected column fields in the row?
3. Join in oData datasource like SharePoint Online List? Validate entries against SPO List Data? SPO list data lookups for dropdowns?
4. Any file upload control and upload to a sharePoint Library? A way to add metadata to a file and do some validation - like does file exist with this metadata. Dynamically rename files to some unique string.
5. Perform complex field validation
6. Secure the application and database to SharePoint groups.
7. What's the business language of choice? Not clear on where to created, edit and save Macros. Can it make calls to webservices?
8. Any way to change that obsure url you get for the App in SharePoint 2013 Online?