The problem imo is the “we should do something else instead FIRST” argument. No. We should do everything we can right now. Usually whenever people start arguing to do something else first, what they actually mean and want is to do nothing at all.
Yes big corporations and their emissions are a big part of the problem but that big ass SUV isn’t fine either. Do what you can as soon as you can. No exceptions.
Smarttube already has something like this. It’s under User interface -> Where to grab card thumbnails. It replaces the thumb nail with a frame from either the beginning, mid or end of the video.