I’m just reading this fantastic news. I definitely agree with @davidak on using semantic versioning for Nix itself (while calendar versioning makes sense for NixOS) so that we can distinguish between major and minor changes. The Rust release model is a great one to follow; they use the concept of editions which are calendar based to segment the usage of breaking changes, while following semantic versioning for the compiler broadly. This produces pretty solid forward and backward compatibility in the compiler.
Overall, +1 to release schedule (rust has been going strong with this!); +1 to master always releasable, that’s what it’s for IMO.