Ironbank was actually doing this before Chainguard existed, and as another mentioned, it's not restricted to DoD and also free to use for anyone, though you do need an account.

My company makes its own competing product that is basically the same thing, and we (and I specifically) were pretty heavily involved in early Platform One. We sell it, but it's basically just a free add-on to existing software subscriptions, an additional inducement to make a purchase, but it costs nothing extra on on its own.

In any case, I applaud Docker. This can be a surprisingly frustrating thing to do, because you can't always just rebase onto your pre-hardened base image and still have everything work, without taking some care to understand the application you're delivering, which is not your application. It was always my biggest complaint with Ironbank and why I would not recommend anyone actually use it. They break containers constantly because hardening to them just means copying binaries out of the upstream image into a UBI container they patch daily to ensure it never has any CVEs. Sometimes this works, but sometimes it doesn't, and it's fairly predictable, like every time Fedora takes a new glibc version that RHEL doesn't have yet, everything that links against starts segfaulting when you try to copy from one to the other. I've told them this many times, but they still don't seem to get it and keep doing it. Plus, they break tags with the daily patching of the same application version, and you can't pin to a sha because Harbor only holds onto three orphaned shas that are no longer associated with a tag.

So short and long of it, I don't know about meat on the bone, but there is real demand and it's getting greater, at least in any kind of government or otherwise regulated business because the government itself is mandating better supply chain provenance. I don't think it entirely makes sense, frankly. The end customers don't seem to understand that, sure, we're signing the container image because we "built" it in the sense that we put together the series of tarballs described by a json file, but we're also delivering an application we didn't develop, on a base image full of upstream GNU/Linux packages we also didn't develop, and though we can assure you all of our employees are US citizens living in CONUS, we're delivering open source software. It's been contributed to by thousands of people from every continent on the planet stretching decades into the past.

Unfortunately, a lot of customers and sales people alike don't really understand how the open source ecosystem works and expect and promise things that are fundamentally impossible. Nonetheless, we can at least deliver the value inherent in patching the non-application components of an image more frequently than whoever creates the application and puts the original image into a public repo. I don't think that's a ton of value, personally, but it's value, and I've seen it done very wrong with Ironbank, so there's value in doing it right.

I suspect it probably has to be a free add-on to some other kind of subscription in most cases, though. It's hard for me to believe it can really be a viable business on its own. I guess Chainguard is getting by somehow, but it also kind of feels like they're an investor darling getting by on the reputations of its founders based on their past work more than the current product. It's the container ecosystem equivalent of selling an enterprise Linux distro, and I guess at least Redhat, SUSE, and Canonical have all managed to do that, but not by just selling the Linux distro. They need other products plus support and professional services.

I think it's a no-brainer for anyone already selling a Linux distro to do this on top of it, though. You've already got the build infrastructure and organizational processes and systems in place.