Some mobile devices will run with a full node. They'll stake and everything.

Other devices (say, dumbphones) that can't run a node will end up using PoBC. The basic idea is:
- dumbphone node contacts other nodes
- provably establishes that the other nodes' blockchains are legit
- thereby proves that a given tx is legit


Why would you say that this is ill-advised? In my view mobile-friendliness is absolutely critical to mainstream adoption.