In my opinion body hair should only be considered as a "last resort" for donor supply. I agree there are not enough cases done to date or published to the hairloss community to able to fully evaluate the yield. In addition the cost can be out of this world so why consider it if one has enough scalp donor.
I have heard of cases as high as 5,000 BHTs but never have seen any pics before/after, never heard of the end result. BH follicules are believed to cycle much slower in the dormant phase so re-growth can take typically up to three times as long. Still I believe it is in infancy, and there's definitely not enough results to base a fair opinion on them, and I am referring to the larger sessions. Now I have seen some good results implanting body hairs into scars that cannot be revised, but these cases were small and calling for delicate repair work, and in most instances the patient lacked any more donor in the scalp that could be safely taken.