"Mainstream" users want a more-selection, less expensive, just as fast variant of iTunes. Frankly, I don't think an illegal filesharing site can scratch that itch and stay in business for long (I'm curious to see how long mulve.com lasts).
If it could, I think a bitcoin-revenue-sharing business model would work well-- "We'll give you 50% of the revenue from any downloads of stuff you upload" (and "we" charge x-bitcoins-per-download).
But I think even if such a service existed there would still be a bunch of people who refuse to pay a bit-penny for downloads. But I agree with lfm-- I think many of them would be willing to pay indirectly for downloads; you just have to tell them that they're paying for "X gigbytes of premium bandwidth" or something...