I think that using the integrity attribute is great because if it happens it's going to have to work through a lot of tricky implementation details (e.g. things like origin laundering) of moving to an internet of content by hash rather than content by location.
However beyond just having an integrity attribute added to html I am interested in the question of how do we encode an immutable url as well as the content-hash for what it points to (as well as additionally required attributes) into a `canonical hash-url` (i.e. encode all these attributes) that is backward compatible with all the current browsers / devices, and which browsers can use in the future to locate an item by hash and/or by location.
The driving reason for this encoding is make sharing of links to resources more resilient, and backwards compatible. Eventually the browsers could parse apart the `canonical hash-url`s and use their own stores for serving the data, but not until the issues (and likely other unthought of ones) listed in the sri addressable caching document you linked are worked through.
One thing that I've found incredibly disappointing about SRI is that it requires CORS. There's some more information here: https://github.com/w3c/webappsec/issues/418 but it essentially means that you can't SRI-pin content on a sketchy/untrustworthy CDN without them putting in work to enable CORS (which, if they're sketchy and untrustworthy, they probably won't do).
The attack that the authors lay out for SRI requiring CORS is legitimate, but incredibly silly - a site could use SRI as an oracle to check the hash value of cross-domain content. You could theoretically use this to brute force secrets on pages, but this is kind of silly because SRI only works with CSS and JavaScript anyway.
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.
To be completely honest: Only reach out if you have solutions for any of the problems or can reduce what you want down to something that is solvable with these problems in mind.
If your solution does not live on the web, you'll have a hard time finding allies in the standards bodies that work on the web :)
You'll have a hard time convincing spec editors and browser vendors already. The working group mailing list is https://lists.w3.org/Archives/Public/public-webappsec/
If you have minimal edits to the spec, we can take it straight to Github. SRI spec contains a link to the repo.