Oh you can very easily break nixos (as in build-break): try to build it from staging, attempt to enable NIX_CFLAGS_COMPILE="-march=native" equivalent, use system-wide LTO or latest gcc, or latest clang. It’s all sorts of broken 
Caveat: that’s what I do as a source of fun bugs to play with.
I call that heating the house in winter
Back when I was young, the same feeling made me jump from Debian to Gentoo. Well, I found what I searched for 
Now I’m very happy with the stability Nixos gives. Hell, I also broke it once and brought back for fun.
Try deploying to completely remote environments without console or IPMI access. Having previous configurations in the boot menu isn’t very helpful if you can’t access them Bonus points if it’s a production system and only reachable over a wireguard VPN.
This is like looking for troubles. I like it.