It'd be great if there were some standardized way to turn older smartphones, whose on-paper computing power is astronomical, into viable Linux servers or controllers.

I've got plenty of old shit phones around that barely respond to touch (or whose displays are just outright unusable) but I'm here considering a new rpi for my next project instead of repurposing one.

There's also a ton of leftover supply of these things, and they have built in power backups, networking, and often lots of shared platform parts (ie, target just one snapdragon based platform and get a swath of compatibility in the galaxy s3 era or whatever).

There is a community effort in the form of postmarketOS but the support for many devices is quite limited https://wiki.postmarketos.org/wiki/Devices

Peripherals using proprietary drivers being the obvious offenders.

Totally cool, but more geared towards rehabilitating old devices than repurposing. Still probably a lot of the work done there could be repurposed (reverse engineered drivers or code for working with a SoC) for plug in server functionality. Thanks for the link, I'll waste some time on it :)

For a server, I feel like termux might be sufficient?

For a server, I likely don't need or even want most of the stuff that's on a stock android install (or even kernel). GPS, audio, graphics drivers, mic, camera, SMS, etc are all worthless at best. Bluetooth (and maybe wifi, if you're USB-plugged) represent explicit unnecessary attack surface for a device that I'll be running with dodgy ported software inside my home network.

Good for proof-of-concepting tho, I bet.

This does remind me that I have a OnePlus 3T laying around in a drawer that would be an excellent degoogled Android device. And my old HTC Dream / Tmobile G1 that I have Android 2.2 on if I wanted a full keyboard...

One of my old smartphones and a portable/folding keyboard would be my pick.

I do love the look of the form-factor though. Want to need it.