Even then as a host you need to provide seeds for all your videos as a P2P swarm will only ever help with currently popular videos. So in actuality P2P ends up with similar hosting costs to traditional video hosting only providing a bandwidth savings on viral content everyone watches simultaneously.
The reality is most people don't need to be able to handle millions of simultaneous views, and so a basic setup with "p2p on top" might work exceedingly well.
My point is the P2P on top is very difficult to actually build and have work well. Like HTTP serving it doesn't obviate storage needs. You need to seed all of the content you distribute via P2P.
Then you're just down to what the CDN cost is for the "active" video, maybe the last two?