I do think that the concept of NixOS has at least the potential for that, but even very basic setups quickly run into edge cases.
Just have an nvidia GPU, which is a solid 75% of users according to at leat the steam hardware survey (which is skewed, but so is the base of potentially interested users), or try to use electron with modern GNOME or KDE, which will be practically anyone who might have an otherwise simple setup. Anyone who is not a programmer likes to use software that doesn’t just sit in nixpkgs IME, too, and often ends up needing to escape the linker (at best, let’s not talk about wine), which is always a can of worms.
On top of this, the nix ecosystem is so full of footguns that I doubt any users who are at that level have a good long-term experience, and the community is largely not very welcoming of complete beginner questions either, as much as some of us try - ultimately they’re frustratingly hard to help without giving a programming 101, which this community just isn’t the right place for; understanding JSON is a much higher bar than it seems.
Sooo… I think your heart is in the right place, and I agree that NixOS could serve as a basis for a kick-ass newbie distro. Even I have to acknowledge that NixOS is not that distro today, though, and unlikely to get there without a good decade of dedicated effort (see snowflakeos for some experimentation in that direction) and a massive shift in general Linux desktop use, and even desktop software vendors. We’ll probably see complete android/iOS domination long before NixOS becomes relevant to a user unwilling/unable to burn a USB with rufus.
Giving branded USBs away at conferences is a cool idea, though, I imagine giving people something physical to remind them to try that fancy distro is a good marketing gimmick, and it’d probably filter for users who are at least receptive to learning if nothing else. Selling such a USB fairly cheaply would let people giving speeches and doing other grassroots efforts get their hands on them to give away, too. Hell, maybe we just need a branded usb and a neat script to let you flash them in bulk (though, security of branded installers remains a concern here, hard to make this safe).
Looking at it from that angle seems like a better perspective for the distro NixOS is today.