Maybe cell phones can be adopted as node (just a thought)....
With wallet pruning it can get down to 2gb which makes it possible. As long as it's still possible to sync on 3G or 4G. Not sure it's really possible to run a full-time node that way though, maybe just to run your own wallet. But maybe.
The R-Pi is basically a cellphone but missing some of the radio stuff. I'm not sure why you would want to do things that way though. It's going to be a battery killer.
There's no reason not to run a full node with proper hardware and a low-cost network connection and access the wallet using RPC calls if you want to be using your own node.
Some people only have mobile to connect to the internet. No PCs, 3G. Lot of people actually. This way they can validate transactions for themselves. Could just sync for personal transactions and run in listen-only for minimum impact. I think it is great that this is now possible -- kudos to Core.