Normalize ribbons between office applications
Ribbons were an OK response to menu creep, but each Office application was optimized separately. Instead they should be optimized for the Office experience, not the Excel or Outlook experience. As an example, there should be one place to find spelling and grammar and it should be the same for every office application. We learn to use office as a whole not individual applications.
In general, common functionality is already on common ribbon tabs in Office. For instance, spelling and grammar are on the Review ribbon tab, across Office.