To my understanding, Ubuntu Core is much similar to the idea of Lennart: http://0pointer.net/blog/revisiting-how-we-put-together-linu...

I don't feel saying them as either bad or good compared to Nix. Until you try a system, there's little to say only from the theory.

We'll see how Ubuntu Core with snappy performs, and this question will be more relevant in a few months.

Nix is not perfect but certainly has a long story maintaining this kind of packaging.