I'd like to see the ability to register ribbon items (tabs and their children) dynamically on the client-side via my app or some tenant scoped javascript that I can register (needs to work with SharePoint Online and should not block submittal to the store). Right now the only way to register a ribbon item of any sort is to do so during the app installation which doesn’t allow us to extend the ribbon over time (either with our own service adding items or by allowing the user to add their own items via an app or whatever).