> And, given their unusual needs and scale, there will probably be some kind of bespoke abstraction, whether it's an SDK, or a document, that says this is the subset of things you should be using, and how to use them, so that we can practically deploy our very unusual setup with different providers and customer facilities.

Now I understand what you meant, I wouldn't have classified this as a bespoke solution since it's more of an operational guide and tooling, most places I worked at running k8s had something similar (a tech radar/best practices of sorts). When I read "bespoke" I thought of "custom built" which I don't think would be the right approach, running k8s and customising the control plane is quite common.