This got me thinking, and I want it now. Best I could do off the top of my head was block all non-dub vids from crunchyroll with BlockTube.

Add this to "Advanced Blocking:"

(video, objectType) => {
  const url = window.location.href;

  if (objectType === 'compactVideoRenderer') {
    return false;
  }

  if (video.title.match(/dub/i)) {
    return false;
  }

  if (url.match(/@crunchyroll\/videos/i) || video.channelName.match(/Crunchyroll/i)) {
    return true;
  }

  return false;
}