Well, the e-ink shipping race is on. I ordered "the good" Waveshare display today: "Waveshare 10.3inch Flexible E-Ink Display HAT for Raspberry Pi 1872×1404 Resolution with Embedded Controller IT8951 Communicating via USB/SPI/I80/I2C" and it's due sometime in early April... as is the M5Paper.
Meanwhile, I've got (nearly) all components collected and mostly soldered and tested for the waveshare-reader build: a 400x240 "Sharp Memory Display", a 512k FRAM SPI breakout, and an I2C GPIO expander, along with two push-button/rotary-encoder knobs, and a tiny 1200mah battery.
The gpio expander might be a mistake: there's enough open pins that I could read the knobs without it, but 1) it has an interrupt pin which is nice and elegant since I can have any input action (knob press or twist) trigger wake-up on a single pin... which is dern convenient, and 2) it provides greater flexibility later by minimizing the pins used on the board, using just I2C and a single extra pin for the interrupt. But it has an obnoxious power wasting LED, which I didn't expect and don't like... I hate to cut into battery life just because I wanted to make the code a little shorter and simpler and keep pins free that I may or may not ever use... hmm... but for now it stays.
The FRAM is added for non-volatile storage with near-infinite rewrites - someplace to store current page numbers for current and recent documents, any data that needs to survive reboots and that changes often to avoid wearing out SD cards or the internal flash.
Tomorrow's project is wiring up and figuring out how to interpret those rotary encoders, and then to start working on a serial shell for transferring and managing files as well as more interesting stuff like receiving and displaying bitmaps in real-time so the device can act as a nifty display panel while it's connected to the laptop.
The state of the build, thus far:
https://pasteboard.co/JRtH5ZX.jpg