I designed a device with an 8" e-ink display recently. I thought it wouldn't be too hard to repurpose it to have it display rendered maps tiles for your current location, using the built-in GPS module. If you could send the device a GPX/KML file over bluetooth, it could plot it over the tiles, and you'd have a simple, robust setup. Searching, entering text etc. are best done on a device with a good input mechanism and data connection, anyway.