I, as someone who worked on the SRI spec find this incredibly disappointing as well. We've tried to reduce this to "must be publicly cachable", but attacks have

I, as someone who worked on the SRI spec find this incredibly disappointing as well. We've tried to reduce this to "must be publicly cachable", but attacks have proven us wrong. And unfortunately, there are too many hosts that make the attack you mention credibly silly: It is not uncommon that the JavaScript served by home routers contains dynamically inserted credentials. And the JSON response from your API is valid JavaScript.