[brandhout]

Deterministic but when the next gcc (or %insert_big_dependency%) update happens all your more obscure packages are broken for a couple of weeks.

[mpalmer]

Don't update immediately? Update immediately, but selectively? Nix offers many options here.

[e3bc54b2]

simply staying on stable channel makes this a non-problem :)

Besides, Nix is even better for such breakages. If GCC breaks you packages, the system does not build and never gets into broken state, all the while old system remains available and kicking.