Full functional parity with all desktop and mobile operating systems.
Microsoft has focused too much on forcing people to Windows. You need to realize that your customers use iOS, Macs, Android etc. All of these operating systems should have the same functionality that Windows gets. This includes Outlook for Mac getting OneDrive integration, full sharing capabilities for the iPad etc. If you want businesses to use OneDrive its going to need to live in a non-Windows world and compete with the Dropboxes of the world.
John, you're right. But guess what... Even Outlook for Windows doesn't have OneDrive integration! (yes, it's unbelievable). MS are very good at selling an eco-system of everything that integrates nicely, but in my 20 years of MS experience, MS products rarely integrate very well compared to third-party products.