One way that SVG could be used for multipage documents is with a convention that the top-level <svg> tag is the document and child <svg> tags are the pages - this is what I do in my app. I also use the fact that gzip files can be created with independently decompressible blocks to create svgz files with page-level random read access [1].

But another barrier is that browsers refuse to support SVG fonts. One supposed reason for this, the lack of hinting support in SVG fonts, is less relevant now with high DPI displays - macOS no longer does hinting at all I believe. The additional effort to support SVG fonts is really minimal [2], so it seems strange that it's intentionally omitted.

[1] https://github.com/styluslabs/ulib/blob/master/miniz_gzip.h

[2] https://github.com/styluslabs/usvg

> What would it take to replace PDF with a zipped html

EPUB. It's already zipped HTML and supports fixed layout.

Or, perhaps more simply, maybe just HTML + paged.js.

> all that is missing is a "page model" for html which would have to be invented.

CSS paged media is already a thing. What else do you need?

There are already page-break attributes for CSS.