Firstly I'd like to signal my agreement with everything Alyssa said. There's nothing here we couldn't live with, and we do want to only make changes that would be good (or worse, neutral) for NetBSD, and never anything that's bad for NetBSD for just Nixpkgs's benefit.
In reply to what Joerg wrote:
I don't think anyone cares at all about the NetBSD target triple means
a.out on some platforms.
Are you saying you agree nobody in 2021 should be relying on this old a.out default?
We do care about not breaking netbsdelf as
that's used on different targets as the canonical target triple.
Yes, absolutely "netbsdelf" should stay as is, and neither of my suggestions for upstream would touch it.