Libp2p or similar stack could be used to provide the phone instance an address, caching could be distributed among peers. Of course, as long as other servers also support libp2p.
What would be the up/downsides?
IIRC Lemmy uses a massive amount of storage
I think it would be, but not in the way you’re thinking.
ActivityPub is based on servers with domain names and accessible IP addresses communicating with each other. It’s mandatory based on the fundamental design of the standard.
So if you were running one of the phones that can run a straight linux distribution, and you connected it to a permanent internet connection as a web server and copy of lemmy with a domain name, then it’s possible. But it’s no longer a phone, it’s a server with the form factor of a phone.
ActivityPub is all about pushing content around to subscribing servers. It sort of expects the subscribers to always be online which would not work for a phone. Servers could resend missed events, but essentially you would miss every event that occurs while the phone is asleep or doesn’t have the app running.
Also, every event that occurs needs to be processed and stored whether or not you are actively looking at it so it would be a huge battery drain while it was running.
It is definitely a service best run on an always-on server with a client application in a phone just asking the server for the latest stuff on-demand.
Its technically possible but not a great idea, lemmy instances take a good chunk of power and storage. And a phone will run out of battery very fast, so you’ll need to charge it permanently, wich will wear out the phone fast. A raspberry pi would be better suited for it.
