You don't have to render the whole page to a pixmap at once; it's very reasonable for a display-list representation of the page using a font atlas to be a tiny fraction of that size, maybe 8 bytes per character, and a GPU shader can render the RGBA pixmap from a spatially partitioned display list on demand. 2144 characters of text on my 1920×1080 display extrapolates to 17152 characters on a 4K display, which would be 140K of display-list data. 0.14 MB is a lot less than 31MB.

(You need additional display-list items for things like the #ff6600 bar at the top and the #f6f6ef background, but those occupy insignificant space even compared to the 2144 characters. The Yahoo/Y-combinator logo and the arrows also add a little bit.)

Of course #notallpages are mostly text, and many of them will require intermediate storage for large photos, <canvas>es, or screenshots of faked Tweets.

If you're on a smaller computer you might render one scan line at a time from a display list consisting of strings rather than individual characters. Those 2144 characters are in 29 lines, so the display list might be under 3K, and a 400-pixel 1-bit-per-pixel scan line is 50 bytes. If you're generating PAL this way you have 64 μs to render each line, which is about 1000–6000 instructions on current microcontrollers, and you can maybe manage 450 color pixels, another 2K or so of raw pixel storage.