I'm actually missing working OLE (Object Linking and Embedding). I used to like it in MS Works in the 90ies: I could insert an area from a Works spreadsheet into a Works document and have it auto-update (you could choose if it should link the data or copy it.)
Within the context of the Microsoft-verse, Fluid Framework (https://fluidframework.com) is supposed to be solving similar problems in web apps, although I haven't personally played with it.
The XML-based surface syntax for HTML5 can seamlessly embed data from arbitrary XML namespaces. It's just a matter of supporting this feature in the browser.