One thing I appreciate about NixOS is the ability to use overlays and override package sources. For example, overlays can be used to selectively install unstable and stable packages alongside each other:
While there may be caveats, this approach has been working for me just fine, as I can install VSCode from unstable to get the most recent monthly releases as they roll out, but then pin the rest of my desktop environment to stable to limit anything else shifting underneath me unexpectedly.