Well, I'd hate to see how that idea would be abused by the people who hate certain anime vids. But yes, I'd back it and vote responsibly. The only problem is that I doubt it would free up much space. A majority of the vids fitting that description are 7mb rm files.
If you cut out everything that breaks the 'no downloaded footage' rule, you'll clear up a lot more space. Most of the 'illegal' high quality download vids are a lot larger than the ones that would be cut out by this voting style. So, if the main goal is to save space and promote the 'downloaded = illegal' rule, then you'd need to do it whole-heartedly, a clean sweep. Still, the voting idea would be a start.