One of the most pertinent questions I've seen on this thread is the "one off or series?" That combined with "Which tradition?" make for interesting debate.

There are so many things you could cover and it would be wonderful to cover as much as possible without making a hash of it - to this end it would be marvellous to get a series together since even a 2 hr one off couldn't possibly do the folk genre justice (certainly if you're planning on covering music, song and dance). If you haven't seen Ken Burns' Jazz series, I suggest you give it a watch since it gave a pretty good overview of the Jazz genre. Of course with folk, you have many centuries to cover, not a mere 100 years. Ken Burns uses an unseen narrator and this works well, I'm not sure that the presenter needs to be seen, and any celebrities who are associated with folk music, tend to only represent a particular bit - e.g. Billy Connolly or any particular musician. You might find a fabulous presenter at one of the summer folk festivals or in a club but I tend to think the story of folk music will tell itself without an individual taking away from it.

So what topics are you thinking of covering?
Morris
Pagan origins of ritual
Story telling
Song collectors
Folk Revival
Folk becomes pop
Folk music and the industrial revolution
Folk instruments
Festivals
Folk celebrities
History
Scottish, Irish, Welsh, Cornish, English, Bluegrass, Romany????? etc. etc.
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I can't think where you'd begin - or end for that matter. But taking a historical perspective could provide and interest for those interested in history as well as music. Whatever you do, Good Luck with it, you will have lots of Mudcat watchers - and could you send me a video to screen in the Auckland (NZ) folk club. ;-)

Cheers F