I want one with an e-ink display. That way I can swap out the e-ink display when I need to for a proper display. That wouldn't work on a normal laptop but should work for their uniquely modular design.
I don't know how well eInk would work for most tasks, though. I mean, sure, it's great for reading documents, and you can do so outside on a sunny day. But most PC software isn't designed to work well with a slow refresh rate.
The battery life savings on an e-reader with an eInk display compared to an LED or LCD screen can be very large, but then the software is designed for it.
If I were only gonna read documents, I think I'd lean towards just loading them onto an eInk e-reader. That just takes, what, a fraction of a minute? Then all the software is designed around the screen's characteristics.
I want to use it programming so I don't get eye strain from staring at a screen all day, and the display is mostly white text on a black background anyway.
Obviously I invert that on an e-ink display. It's white on black is to reduce the amount of white light that I get blasted with. When you're programming most of the screen is blank because each individual line of code isn't really that long in most cases it'll be shorter than in English sentence.