Yeah, with systemd, it’s a bit more complicated.
systemd-stable is a nice way to receive (security) fixes and minor bumps, which I’m feeling generally okay to backport to NixOS stable too (if it’s only a minor bump) - but I’m actually not sure how many major versions back still receive these fixes - stable shouldn’t run on an already unsupported release.
In any case, there needs to be some place receiving major systemd bumps quickly, uncovering issues with higher-level tooling and potentially fixing any fallouts, and I feel like this is what only nixos-unstable can be - but this shouldn’t delay/risk stable releases.
Maybe we need a longer stabilization period / earlier branchoff from nixos-unstable, and be less afraid to revert things there if it looks like regressions can’t be fixed in time?
Also, it might make sense to align release schedules to those of other distros, so they also run into these issues during their stabilization periods - and we’re not the first ones running into these issues alone 