It would be amazing if gaming broadcasters could stream directly to their subscribers/followers, with very little latency (not the 30 second video lag Twitch adds). Broadcaster monetizing could be tricky, but definitely doable.
And honestly, if you were streaming a 1080p video over p2p, I see no physical way that it would be below a 30s delay if there was 1k+ people watching it.
You are limited by peers outbound bandwidth and for most in the US that is going to be sub 5MB/s. With that in mind, you can really only have a maximum of 5 or less streams per user. That means to get to the 1000th viewer, its going to be a daisy chain of 50+ users in front of you before you get the data.
P2P does not and can not work for distributed video until home connections catch up. (Unless you are OK with insane delays)
Obviously in practice you wouldn't get a perfectly balanced tree, but I don't see where your "50+ users" is coming from.
Delay matters most in case of live betting and live score. There is whole industry around this, I am sure you've heard about bwin.com or bet365.com.
Delay matters when multiple people are trying to watch the same stream "together", but end up seeing wildly different points of time in that stream.
Additionally, broadcasters can still do Paypal donation links, like they do over at Twitch.
Advertisements playing before videos, I'm not sure how it could be done, but it probably could be an overlay before the stream starts, or just a HTML5 video that loads first and must finish before the P2P stream begins.
Revenue streams come from supporting the back-end telcos (billing, active traffic mgmt & shaping), and content generators (disney/pixar etc), and a couple of other things I'm not ready to talk about just yet ;-).