Nix / NixOS

The flakes interface of nix may change in the future, and you should be prepared to update your code, documentation etc. if and when that happens. Consider flakes have been around since nix 2.4 and the interface haven't drastically changed since then. If that risk sounds acceptable to you, then do use it :)

There is an ongoing effort to get flakes away from the experimental category, but as you may guess, it is a big chunk to stabilize all at once. The original RFC was closed https://github.com/NixOS/rfcs/pull/49 a long while ago, due to it describing the experimental feature, and not the final one. AFAIK, there's no "one" RFC being discussed on finalizing an initial stable version of flakes (but I could swear I've heard of one).

Yes. The format is widely accepted by the community and generally everybody's preferred way of organizing and sharing code.

I quite like flakes on the whole, but there is still, in my opinion, a pretty big unsolved issue, in that it's impossible to configure a flake. Some consider it a feature, and in some sense it is, but at the same time it incurs some pretty hefty drawbacks (admittedly, these are much more relevant for using nix as a build tool rather than as a package manager for an OS).