It seems like there are broadly 2 concerns: having rich interaction inside of a single "page", and smooth transitions between "pages". You seem to dismiss the latter in your article, but HTMX seems to support Turbolinks style functionality, correct? Can animations be layered onto that?

I did some experiments around on how to do animated shared element transitions (as well as reactive functionality) within a REST mindset here, if anyone's curious: https://dev.to/eshan/toward-the-postmodern-web-38h (you can just scroll to the embeds)

Ultimately, maybe the browser vendors will do something here, like Google's portal elements, for example. A lot of effort is being spent on that flash during page loads.