I think it depends on what they want it for. I can imagine NixOS being perfect for user workstations for example, as an alternative to Windows workstations managed with Active Directory.

I imagine you have a lot more experience than I do packaging for NixOS and other distros given your product, but in the few cases that I've needed to run a binary, I just wrap it with a flake and it's done. I also stay on NixOS stable, so I avoid the sharp parts of "bleeding edge". In my experience as a desktop user, I've never had a failed rollback since using NixOS as my primary OS since around 2016. However, whenever I try to use it as a server OS, I often do hit the pain point you mentioned around statefulness. More specifically, the happy path is extremely happy, but once you need something off the happy path, you find yourself creating some really ugly glue to get it to interface with the happy path. The pattern I've settled on is using Podman quadlets for most services, but that isn't without pain either. Then you find that you've become a Unix sysadmin, managing different UIDs for rootless podman, different network domains, dealing with permissions issues, etc. I'm currently experimenting with microvm.nix to see if that will be cleaner, but no conclusions yet.