It drives me NUTS that nobody makes a decent e-ink device with a GPS app.
It seems like it'd be ideal for the backcountry use-case. Super long battery life because you could just wake up the GPS every few hours and get a new fix, reframe the map, then go back to sleep and use the latent image like a topo map.
I have a few use cases like this that would go towards replacing my phone. I'm on the lookout for a hackable/linux ereader.
I thought the reMarkable was that, but they hardware-disabled the Bluetooth radio in the wifi/bt chipset, and that really wrecked most of my use-cases.