I think we are talking about repurposing a small computer previously used as a mobile handset into a server. This is already possible and done with Android and Linux handsets. It is just not as straightforward as using a RPI with a distribution such as Yunohost.org. It's scalability is also very limited, but it kind of fits the low power low cost factors of the RPI.
No, nobody was talking about that. The context was clearly one's personal Android phone (in the article), and "your smartphone" in the original comment (not "an extra/old"). The one you carry with you all the time. The article even admitted you'd have to "carry an extra battery".
OK. There are P2P mobile based social media services such as https://www.manyver.se/ already running. Although every node is serving/getting messages, I am not sure they can be called servers.
No, I - as the OP - said also "pocket computer" very explicitly. If a 'personal mobile server' would become reality, it's not going to be a smartphone + something else on top.
Ok, but yes it would still be cool if any of these devices, whatever you want to call them, could be plugged in somewhere and act as a server.
> (not "an extra/old").
So then you concede completely, that anyone talking about these devices, would indeed be correct to say that it is cool to turn these devices into servers.
Great, you agree that there is a usecases for this.