Even if you're looking at mobile displays, there's a finite set, and those can either be punted or targeted precisely at the 4", 5", 6", 8", and 10" device sizes which are most common.
Using an e-ink device, I'd really prefer more Web content were paginated. I tend to rely on the EinkBro web browser for anything over a page or two in length simply because I can page through that rather than deal with the fussiness of scrolling.
Once you reach a sufficiently large display, physical pragmatics come to the fore. We've settled on books that are mostly 8--14" or so diagonal measure because that's what's convenient to hold and read. There are smaller and larger exceptions (pocketbooks and other miniatures, coffee-table books and atlases), but those are 1) less convenient and 2) clear compromises between format, material, ease of reading, and other factors.
For a sufficiently-large desktop display, a standard quarto/folio print format displayed 2-up is usually preferable. Scaling from that or presenting 1-up is really the desktop / window manager's problem.