I don't use PyPI and only skimmed the docs. I think what you're saying here makes sense, but I also think others posting have valid concerns.
As a package consumer, I agree with what you've said. I would have a preference for packages that are built by a large, trusted provider. However, if I'm a package developer, the idea worries me a bit. I think the concerns others are raising are pragmatic because once a majority of developers start taking the easy path by choosing (ex) GitHub Actions, that becomes the de-facto standard and your options as a developer are to participate or be left out.
The problem for me is that I've seen the same scenario play out many times. No one is "forced" to use the options controlled by corporate interests, but that's where all the development effort is allocated and, as time goes on, the open source and independent options will simply disappear due the waning popularity that's caused by being more complex than the easier, corporate backed options.
At that point, you're picking platform winners because distribution by any other means becomes untenable or, even worse, forbidden if you decide that only attested packages are trustworthy and drop support for other means of publishing. Those platforms will end up with enormous control over what type of development is allowed. We have good examples of how it's bad for both developers and consumers too. Apple's App Store is the obvious one, but uBlock Origin is even better. In my opinion, Google changed their platform (Chrome) to break ad blockers.
I worry that future maintainers aren't guaranteed to share your ideals. How open is Open Solaris these days? MySQL? OpenOffice?
I think the development community would end up in a much stronger position if all of these systems started with an option for self-hosted, domain based attestations. What's more trustworthy in your mind; 1) this package was built and published by ublockorigin.com or 2) this package was built and published by GitHub Actions?
Can an impersonator gain trust by publishing via GitHub actions? What do the uninformed masses trust more? 1) an un-attested package from gorhill/uBlock, which is a user without a verified URL, etc. or 2) an attested package from ublockofficial/ublockofficial, which could be set up as an organization with ublockofficial.com as a verified URL?
I know uBlock Origin has nothing to do with PyPI, but it's the best example to make my point. The point being that attesting to a build tool-chain that happens to be run by a non-verifying identity provider doesn't solve all the problems related to identity, impersonation, etc.. At worst, it provides a false sense of trust because an attested package sounds like it's trustworthy, but it doesn't do anything to verify the trustworthiness of the source, does it?
I guess I think the term "Trusted Publisher" is wrong. Who's the publisher of uBlock Origin? Is it GitHub Actions or gorhill or Raymond Hill or ublockorigin.com? As a user, I would prefer to see an attestation from ublockorigin.com if I'm concerned about trustworthiness and only get to see one attestation. I know who that is, I trust them, and I don't care as much about the technology they're using behind the scenes to deliver the product because they have a proven track record of being trustworthy.
That said, I do agree with your point about gaining popularity and compromises that developers without an existing reputation may need to make. In those cases, I like the idea of having the option of getting a platform attestation since it adds some trustworthiness to the supply chain, but I don't think it should be labelled as more than that and I think it works better as one of many attestations where additional attestations could be used to provide better guarantees around identity.
Skimming the provenance link [1] in the docs, it says:
> It’s the verifiable information about software artifacts describing where, when and how something was produced.
Isn't who is responsible for an artifact the most important thing? Bad actors can use the same platforms and tooling as everyone else, so, while I agree that platform attestations are useful, I don't understand how they're much more than a verified (ex) "Built using GitHub" stamp.
To be clear, I think it's useful, but I hope it doesn't get mistakenly used as a way of automatically assuming project owners are trustworthy. It's also possible I've completely misunderstood the goals since I usually do better at evaluating things if I can try them and I don't publish anything to PyPI.
1. https://slsa.dev/spec/v1.0/provenance