I'd be curious to have your perspective on the risks of relying on 3rd party infrastructure. That 3rd party can't really try to feed wrong blocks or transactions, it would ruin its business. Then from a practical standpoint, the only attack it can run is a Sybil attack which, when not spending any transaction, can't result in double-spends. So what do you see as a problem relying on 3rd party infra for Bitcoin development?