Another option: a touchscreen, but with a mechanical backlight. What I mean by that is a little string you pull that spins a magneto that momentarily powers the backlight, maybe for 5-10 seconds at a time. This frees the battery from a major source of drain (hopefully comparable to e-ink) and also has a built-in limit to how much screen time you get. Eventually anyone would get tired of pulling the string. But it would be plenty for a map or sending a text or email.