I'd just like to interject for a moment. What you're referring to as the NixOS stable branch, is in fact, duplication of efforts that should go into `nixos-unstable`, or as I've recently taken to calling it, the QA mirage.

The stable branch is not a proper, long-term supported component unto itself, but rather a temporary, five-month snapshot of nixos-unstable made functionally useless by the lack of additional tests and the fact that no extra QA is run compared to unstable. All the backporting effort is trashed when the next stable branch is cut from a fresh, future point in nixos-unstable.

Through a peculiar turn of events, the branch widely considered "stable" today is often just called "stable," and many of its users are not aware that it is basically the same system, but one that actively wastes the community's time by forcing them to re-land fixes on a branch that will soon be deprecated. There really is a stable branch, and these people are using it, but it is just a cyclical dead end in the system they use, offering no genuine stability guarantee beyond what `nixos-unstable` already provides.