The intent is not for most ETH to be staked. 12-13% is fine, and they don't expect it to go beyond 30% or so. We just need enough staked so the network is secure.
Staked ETH isn't available to be used for any other purpose, like paying transaction fees, depositing in defi protocols, using as currency, etc.
Anyway, this is getting a bit far afield of my point, which is just that for ETH, exchanges can earn money on deposits, without loaning them out to risky side ventures.
You mean whether it's a viable model for the exchange? I have no idea, never looked at their numbers. But Coinbase is public, so now I'm curious whether they break out their revenue sources.
So there are still a lot of unknown unknowns, including ‘what will the ecosystem look like when it is the majority’.
It might be lower on fraud. Or higher. Or economic to just stake. Or not.
We don’t know yet.