I know you can do that for blindness, but the challenge I see is gaining a good understanding of how people would actually navigate a site. For instance, perhaps someone who is legally blind might use a screen reader, or just magnification, depending on their preference.

From what I've read, screen readers are typically played at a very high speed (once you get used to it) - I don't know how you'd know things like that without advice from the people using them.

The second question is how you're supposed to navigate if you can't see the text well or at all - this might require adding features to the HTML to integrate with the screen reader.

I can visualize what my website looks like already, so if I shut my eyes I'd just be navigating it in my head.