I imagine part of the challenge going forward would be the hordes of programmers brought up on designing UIs using a DOM, and all the associated tooling.

My prediction is the situation could be similar to how today many text-only programs assumes a terminal-like device. Terminals have been obsolete for years but I personally feel it's a ball-and-chain on text UI development. The web document model could persist long after web browsers are a kind of "terminal" to load and render web documents.