[rep_lodsb]

A lot of that is just bloat that you wouldn't have had back then. But it could still be handled by an 8086, not by storing the raw HTML in memory at all, but parsing it as it loads. Each DOM node would be its own object with child pointers, with attributes and names all converted into binary numbers of (at most) 32 bits each.

64K of actual text content in a single node could be reached in some documents, but it's not that small, more than a chapter of a typical book.

What was always a problem for segmented memory was graphics, at least if you wanted higher resolution than 320x200 at 256 colors. But you could have a segment pointer to each row of pixels instead of an entire image, as long as it would still fit within 1 MB (16 MB in the 286 protected mode).

[AKSF_Ackermann]

True, graphics is a better example of a period-correct >=64k work, but the point is that there are multiple things where you don't expect the data to be that big until it suddenly is.