My biggest frustration with Nix is the lack of typing. Writing anything more than the basics, I feel like I quickly run into an issue of not being able to reason easily about what structures I'm manipulating, and I haven't gotten very far by trying to lean on the editor I'm using either.
There's some prospect of Nickel (https://github.com/tweag/nickel) meeting this need, though haven't tried it and can't really vouch.
Typing might be really helpful for building your own layers up, but I don't know if it can meaningfully help with problems around consuming existing Nix ~APIs.
