The idea proposed here is to allow read-only access to an origin's (e.g., buyer's) interest groups within a Shared Storage worklet. From the worklet, you could send out private aggregate reports (e.g., create histograms) based on the IGs you've created for the given user.

Use cases I could imagine include things like, understanding how many IGs your users have, how valuable they are, how often IGs might conflict, etc. It seems like something that would be useful to ad-tech to understand what's happening on device by looking at all of their IGs collectively.

Would this be useful to you? Please let me know if so.

Pseudocode example:

Advertiser page:

navigator.joinAdInterestGroup({owner:"a.com", name: "foo"});
navigator.joinAdInterestGroup({owner:"a.com", name: "bar"});

let worklet = await sharedStorage.createWorklet("https://a.com/worklet_metrics.js". {readsIGs: true});
worklet.run("processIgs");

worklet_metrics.js

class IGReporter {
  async run(data) {
    let igs = await sharedStorage.getIGs();

    // Record how many igs the user has.
    privateAggregation.contributeToHistogram({bucket: igs.length, value: 1});
   }
}
register('processIgs', IGReporter);