Require each packager to seed = require them to be always on, and to have a fast upload connection. That would be a big hurdle IMHO, with the caps, per-mb charges and even the always-on requirement.
The main isos already have torrents, not officially posted ones but with md5sum you can be sure they're genuine. (though I don't get why, when they are both small and can max one's download by using more than one mirror and aria2).