> Example: Using Next.js again, out of the box it does instant navigation by preloading new content on hover, and not doing full refreshes when they aren't needed. Great for the user, less bandwidth used, much faster sites. That's just one example.

I don't understand what you mean here. What content is being preloaded, what is being hovered on, why do you need only partial page loads? Is this for a doomscrolling UI where units of content are presented one or a few at a time, on an infinite scroll?

When I do navigation I just build a <ul> and put <li>s in it, programmatically if need be. Click to go where you want. Takes a full page load, but that's just how the Web works because you're going to another page. Links take you to other pages.

Is this for like an image gallery?