It might not be possible to auto-detect the root device in very complex cases (custom dual boot setups, network boot) but how about auto detection for the most common cases such as common environments set up by the Fedora or Debian installers?

Maybe dracut developers think root device auto detection bad idea? Maybe it's considered insecure as it risks booting the wrong device? If so, they probably have a valid point. Then how about auto detection of potential root devices but prompt the user before booting from an auto detected root device? Or otherwise provide more guidance than a dracut rescue shell?

That seems better to me than dropping to a dracut rescue shell. A situation most users will be stuck with.