Why are you assuming the result will be a "hodgepodge" or "tangled mess of wires"? Unless you take it apart, you won't be able to tell if a product runs on a bespoke PCB with SoC, a Raspberry Pi, or an old phone's hardware. Plenty of commercial hardware today is just an Android phone with some custom apps and system modifications, only it's generally a new, expensive, "enterprise-ready" device.

> There's a dozen apps that allow your phone to be repurposed as cameras or GPS trackers today, what's holding back their adoption?

Personally I think it's the lack of control over devices that's hindering these apps. A common modern phone doesn't let you replace the system UI with some purpose-built app, it doesn't let you run without a battery, it doesn't even let you disable all notifications. The result just isn't up to snuff unless the user/device manufacturer has full access to reduce the system to just the parts they need.

> If you read my initial comment you'd see it states in no uncertain terms that I'm skeptical of the argument that it'll meaningfully reduce e-waste, ...

And you haven't provided any meaningful counterargument so far. You still seem to be under the impression that reusing phones means hobbyists "gluing phones" places, but that's far from what I'm advocating.