Up until this point we have always understood content through the lens of the distribution channel it sat within. The channel, in fact, gave its name to the content (TV is a form of distribution but we think of it as a form of content) - or, as per your reference to McLuhan, "the medium was the message". The social media revolution is all about the liberation of content from its means of distribution and we therefore need to stop using distribution (TV, Twitter, Mobile) words to define and imprison what is simply video content. Does this also mean that the message is also the medium as you say? I am not sure, it seems more a case of the medium simply becoming irrelevant.
In the future there will be many types of video content - and the content itself will find the distribution channels most appropriate to it, rather than being defined by dependence on a particular channel. What we currently call TV content won't be defined by sitting in a TV channel, but will instead be defined entirely on account of its context - real-time, interactive content, whose relevance depends on it being seen by lots of people all at the same time (sports, news, interactive entertainment such as Pop Idol / X Factor). The requirement to be seen by lots of people in real-time will define the channels it get's delivered by.
Is this Social TV? I don't know - but I think we should drop the TV word or else accept that TV simply becomes a label that is attached to one form of video content. Or else recognise that TV is neither content or distribution, but simply a business model. I prefer to think about this whole issue in terms of Social Video.