Thank you for writing this. I had this feeling that the document model isn't that bad for software in the first place (a feeling that I noticed when I prototyped some of the stuff I was working on in Observable, and realized the prototype in an interactive notebook format fits the problem more than the SPA we were building). But I haven't considered the implications. You might be very right that the document model could support a lot more than we give it credit for, if we just stopped pushing the established "appliance" UI paradigm.