Custom CLI-based Warnings for Sub-Registries

[benderTheCrime]

I don't know that I would call this a substantial feature request, but it would certainly depend on the status of this issue:

npm/npm#19249

I would like to implement something similar for Yarn to what is described in that issue/feature request for npm:

My intent is to allow for custom registries to use npm to warn based on their own criteria and a well-defined schema. I was thinking this could be a new optional property on the returned data from the NPM "/package" and "/package/version" endpoints "warnings" or "genericWarnings" which was an Array of Objects possessing at least a "message" property. The CLI could read the presence of this key and then log out any necessary warnings.

Since Yarn works based on the npm registry, this would depend on the presence of the added "packageWarnings" or "genericWarnings" keys in the registry itself, unless someone was to use Yarn with a sub-registry, which is my intent.

I've looked at the source and I cannot find anything other than the engine-based warnings and some other CLI-internals.

Question is: is this something that already exists? If it does not, is it a suitably small feature request? I do not mind implementing this myself.