I think radio 4 is the place for it. There always will be a documentary aspect to folk music as a subject, even if all the tracks that are played are contemporary, and this means Radio 4 to me. Also it's only Radio 4 and Planet Rock that I have programmed in on my digital radio!
The reason I never listen to Mike Harding is that I'm never reminded that it is on, as it's on Radio 2 and not trailed on Radio 4.
The reason that I have trouble in listening to "The drift" on BBC Radio Lancashire is that it's on the same night as we have the best session for miles around and I'm usually getting all the chores out of the way ready to go out.