The "club" in "folk club" means "society" in England. Not like the club in night club, or working-man's club, which means a premises.
Folk clubs in England are just organisations that meet in rooms in pubs once a week or whatever.
   I have seen traditional black African music, and traditional Kurdish music, in English folk clubs recently, but only when I have made a positive effort to organise the visit (by persuading the club organisers that it would be a good idea to have some different coloured guests). In each case the reception was fantastic, but I really dont see this sort of thing catching on, alas. Liking music from other cultures is always, I suspect, going to be a minority interest. And, with black people in England, this means a minority of a minority, which will (as has been pointed out) become vanishingly smal in an audience of 20-50 people: which is what you get in a folk club.
   If the clubs want multi-cultural audiences, they need to book multi-cultural acts.