Obviously you'd have to replace the OS with an up-to-date one to use the phone as a cluster node.

But... if Google can do so if handed a random pile of old phones, then why would a consumer not be given the same option for their phones? If it works only for phones sold by Google once, same question holds. And applies to other vendors.

As you said: the "phone becomes useless just because OEM drops support" cycle needs to be broken. Well.. that and ability for end-users to replace batteries, screen, fix connectors etc.

Also it's unclear how data would move in & out of these old-phone-compute-nodes. USB-C? Article is a bit light on details there.

The lack of open, replaceable software is the main blocker. The article talks about only keeping the motherboard anyway.

End users don’t need to replace screens, ports and batteries if there is reasonable cost parts and skilled labour available.

I’m happy with a trade off where a device has extreme miniaturisation and water resistance but needs someone with some surface mount soldering skill and the right tools to work on it.

Regardless, many (most?) phones hardware will last longer than the software running on it.