I dream of a lightweight e-ink typewriter. Sometimes I want to write without all the distraction of the "normal" devices.
$500 for a mechanical keyboard strapped to an eink display. Syncs with Dropbox. Sounds right up your alley.
But I guess "about 15 hours" sounds a lot less impressive than "3-4 weeks".
https://en.wikipedia.org/wiki/TRS-80_Model_100
Though maybe it's not quite as light as you were hoping (at least, not by modern standards)