Sometime ago I had an idea that SPAs exist mostly because animated transitions between pages make managers happy, not to serve any actual user need. If that's true, maybe we could add support for animated transitions between server-side rendered pages, and make SPAs mostly go away.

Then I realized we could do that easily with a JS library! We could give some divs a "sticky-id" attribute, so they stay as part of the DOM tree when the page reloads, only their contents get replaced with the contents of divs from the new page having the same "sticky-id". That way there's no flash to white, and CSS transitions on sticky elements get a chance to fire. The whole thing could be handled by a generic onclick handler on each link. And the links would support opening in new tab as well, the JS would only fire when they are clicked in the same tab. I think that would be the most conservative way to have an SPA-like experience with a minimum of JS. Unfortunately I was too lazy to implement it :-/

EDIT: It's interesting that most replies to this comment seem to talk about whole page transitions, like fading out the whole page. But as I envisioned it, the key part of the idea is that we can get element-by-element transitions without writing custom JS, just by adding "sticky-id" attribute to some elements and letting their CSS transitions do the work.