But the whole point of this project is to appeal to the mass market, and give smartphones a ten-year life cycle. They're explicitly aiming at a much wider userbase than hackers alone.
No, the whole point of this project is to be able to use your 10 year old phone for other things, like a mini-computer, or a Pi.
You run a newer build of Lineage or CarbonRom or whatever on an old phone and it will most likely run like crap (current LineageOS on an old Sony Xperia Z 1st gen for example, is a terrible experience).
But that phone still has a ton of power. It's more than capable of being better than an early 2000s laptop. If you can stick Linux on it, it can be an embedded device. Get Wayland working and you get a little screen you can use for projects.
This has the potential to turn a lot of obsolete phones into powerful little hobby machines.
Do you think that hackers as a market aren't, by near definition, early adopters and want new technology? I don't know who else a 10 year old phone would appeal to but parts of the mass market?
(Some) Hackers are also the kind of people who keep their hardware around for ages and run strange OSes if it fits their needs, because they want daily tools to work, reliably and like they always did. Tinkering can happen on top of that or with less important things.
Yup. I'm running a four year old phone because it does what I want and newer phones don't. Money isn't even an issue, there just isn't choice out there today.