To OP: having an old version of android is generally a good for a e-ink device. Newer versions add things that aren't needed and restrict some others that are cool to have (like full filesystem permissions).
An eink device with android 4.4 - 6.0 is still good nowadays. All ebook reading apps that I'm aware work fine in these versions. Other tools, like dictionaries, rss readers, file managers... work too.
I would like to see a barebones AOSP e-ink device, without Google Play Services and no google apps, based on Freescale SoC and heavily optimized for battery - specially suspend behaviour. A big plus would be return back to USB mass storage instead of MTP.
I would buy a device like that without doubt, download some apks from Fdroid and get ready to read.
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