I'm awaiting the arrival of what is purported to be the definitive book on the subject:
Uncle Tom Cobley and All by Todd Gray. As soon as I've read it I'll report back.

My interest stems mainly from its possible relationship to a much wider-spread older song 'The Old Grey Mare' (Roud 680). It would appear that WF is an adaptation of this as they both contain taking the mare to the fair, the mare going up ----Hill and making her will, dying and the owner crying.

If the book doesn't make the connection I shall probably write an article on the connections.