Would it really work? I think you'd have to rewrite some parts of the kernel, but I may be wrong now, in the past or the future.
Anyways, we're arguing semantics here, it'd be better for all to separate udev from systemd. It's like Windows installers usually bundling the program with some crap, and I know most people don't appreciate that.
Yes, and udev would compose an hypothetical "Udev/Linux system". But Linux itself doesn't need udev.
GNU / GCC is different because you literally can't compile Linux without it. But if and when LLVMLinux succeeds, I don't think you could say the same.