I though about that, it is technically possible. More than that, it is relatively cheap (incoming traffic on most VPS is free). Still, I decided that searching by file size is much more cost effective. It is almost as good as searching by hash for larger files. It requires little to no code and time to implement. It is available even for torrents without seeds. It doesn't involve downloding files (which, in some people opinion, is illegal as such, even if you don't actually see the downloaded files).