Yeah, the projects I've heard about that have done something like this broke it into multiples.

For example, 1000GB could be broken into forty 25GB torrents and within that, you can tell the client to only download some of the files.

At scale, a webpage can show the seed/leach numbers and averages foe each torrent over a time period to give an idea of what is well mirrored and what people can shore up. You could also change which torrent is shown as the top download when people go to the contributor page and say they want to help host it ensuring a better distribution.

Since I'm spamming with this same idea right now - the description is similar to Freenet (the old one, the Hyphanet), but you'd need some kind of ability to choose parts of which collections of data get stored in your contributed storage, while with Freenet it's all the network (unless you form a separated F2F net, there is such an option, but no way to be sure that all peers, ahem, store only IA data and not their own porn collections, for example, taking precious storage). I've described one idea in my previous comment, but it's purely an idea, I'm nowhere close to having the knowledge to make such.