dd_
An upcoming feature of nix is content addressed builds which use the output hashes to determine the store path. This should make it much more transparent which builds are reproducible and which are not.
Another thing that comes to mind is the ability to parametrize flakes so that they can be configured from the CLI: https://github.com/NixOS/nix/pull/6583
As for keeping up with PRs and other responsibilities, that seems to be one of the stated goals of the this new Nix Team. I guess we'll see how they intend to handle this soon.
With flakes, it is now significantly easier to create an standalone package or module for your specific needs since you import it just like nixpkgs. It also means that software doesn't have to be part of nixpkgs to be usable on the system - if a git repo has a flake it's just a matter of adding it as an input. Flakes represent such a massive improvement to the way that you interact with nix, I sincerely hope they become the default here soon. In the meantime, it is well worth your effort to learn them even if they aren't 'required' yet.
Unfortunately all of this is contingent on being able to grok the language in the first place which is where the documentation really falters. The nix pills talk about the basics of the language but it is very difficult to make anything useful without importing some libraries (i.e. nixpkgs) - and these libraries are not very well documented. I am aware of a documentation team being formed to help address this but it still remains the number one issue with nix, especially for newcomers. The unfortunate thing is that there are so many moving parts that it will take a considerable effort to explain the entire ecosystem without being overwhelming but still providing enough intuition for newcomers to get things done with Nix.
If anyone is interested, a recent SoN talk was given about efforts to improve the documentation. It touches on many of the things I bought up here: https://www.youtube.com/watch?v=WFRQvkfPoDI
Despite the reputation, I feel that NixOS or some derivative of it has the power to become the best distribution for non-technical users in the long run. What NixOS has done is effectively built an interface to every component of a modern Linux system, all that needs to be built is a user application to take advantage of it. Of course, there still needs be some improvements in Nix itself for it to blossom into its final form, but I really see a path to greatness here.
I have often thought about creating a simple unified Win2K-esq or BeOS-like X11 WM/DE specifically for NixOS but unfortunately I lack the time/motivation.