Agreed - although I came to the same sorts of realisations through Guix, the fundaments of the projects are the same (as I presume and hope you and other Nix people know). So the answer is Nix and its spiritual sibling, Guix, and any other project that attempts to implement the meat of that thesis there (which I hadn't seen actually - thank you!).

I feel there's a surprisingly strong standoffishness between the two communities of users, but that's a side point.

On topic though, for example, https://guix.gnu.org/en/blog/2020/reproducible-computations-..., and there are other excellent posts on the Guix blog going in to great detail on the topic of reproducibility and the efforts they are putting in there.