[bpmct]

For those on a budget, I highly recommend checking eBay for old e-ink readers. Many of them can be rooted and are by far the most affordable way to get e-ink (plus compute).

The Nook Simple Touch is one of my favorites

[normie3000]

How is the Nook Simple Touch dev scene these days? Is there any functional alternative to a very old Android version?

[bpmct]

Not that I'm aware of, but there are some great projects on the XDA Forums and GitHub I was able to reference in order to make basic apps for Android 2.1.

e.g: https://github.com/usetrmnl/trmnl-nook-simple-touch