Embedding Video from sites other than youtube?

It requires an add-on to be installed to the forum software, if another site became hugely popular and allowed embedding I imagine the administrators would consider adding that to the site. It's unlikely they'll allow videos from any site to be embedded though, depending on how they did it, that could open up vulnerabilities with people posting HTML code.
 
You Tube only at the moment mainly for security reasons. Not impossible in the future but don't hold your breath.
 
Its possible but unlikely given that a vast majority of video still comes from YouTube.