Are you nuts‽ Every unwashed, scrofulous, snarky nerf herder will flock to PM to make YouTube-ish Anonymous posts, which would be a blight on the elevated S/N ratio of the PM ecosystem, unconstrained by any socialized sense of guilt over non-normative expression of views attached to a fictitious on-line persona and we must forestall that since no one ever ignores the anonymous posts!!!
No, I don't mind other video servers and others might find it better to have a non-YouTube alternative. For example, the dimwit CIO at my company has forbidden all YouTube links, so the likelihood of listening to perl broadcasts actually goes up for me if hosted from other servers, e.g., Vimeo.
Yes, I think linking PM threads to off-site videos is a good experiment. It is a nice step-out for a mashup of PM with other on-line sources.
By mail forwarding, do you mean notification of comments on a thread? That is, something beyond the chatterbox notifications you get when you have replies to a post? (Hey, is there an anonymous mail drop where we can see responses to anonymous posts? It would be a hoot to see all the responses to all the posts that I don't remember writing.)