OK, I've finally got round to boiling my FMJ article down to the essential points. Here goes:

1.  The ultimate source of TWR is almost certainly be Thomas Lanfiere's 'The Goodfellow's Resolution' from the late 17th century, one of a number of moralistic broadsides of the period describing the wayward behaviour and subsequent regrets of 'Bad Husbands' and the treachery of alewives (landladies). TGR is the only one of the 'Bad Husband' ballads to feature the deception of the landlady regarding the customer's financial means. It's been discussed here before - see here.

2.  Lanfiere's 13-verse text was edited and condensed, appearing in late 18th / early 19th chapbooks and broadsides, with the 'Bad Husband' being converted to a 'Wild Rover' along the way. Different stages in the evolution are preserved in these print versions, which had found their way into English oral tradition (sung to a different tune from the familiar one) by the early 19th century, when a harmonized version crops up in Thomas Hardy's grandfather's songbook. The song was also reproduced in American songsters, mid-19th C, and was extremely popular in Australia – where three different strains and a Country & Western rewrite all did the rounds.

3.  At some point the 'No, Nay, Never' chorus replaced the earlier 'Wild Rover, Wild Rover' form - I located (thanks, Jack Campin) only one, very late, broadside copy from Scotland including the NNN refrain, but it was present in versions collected orally in Scotland by the early 20th century which were distinctly different from the Hardy copy.

4.  The 'prodigal son' verse appears probably late 19th century and, together with 'No, Nay, Never', sweeps the board, the modified song appearing in oral versions from Scotland, England and Ireland through the early-mid 20th C.  It was popular in Yorkshire pub sings in the early 1960s, before the Dubliners or Clancys released their versions. The tune seems to arrive at something like the familiar one by this point, although one Irish variant has a lovely modal tune completely unlike the regular one.

5.  Louis Killen hears a version on BBC radio in the 1940s, remembers it later, and adds it to his repertoire, padded out with source singer Sam Larner's words (this information comes from responses given by Louisa Jo Killen in the year before her death).  The BBC version seems to have come from Nova Scotia (the alehouse is in 'Halifax Port') and has the extended chorus – dwelling for three beats each on 'No', 'Nay' and 'Never', followed by a gap - that we're now familiar with (it doesn't occur in any other oral version). It was apparently 'collected' by BBC producer Jack Dillon on board a ship bound for Russia (where he was heading to fight in the civil war) in 1919. The Vaughan Williams Library has a 78rpm record of the song as Killen heard it, sung by a BBC baritone with small orchestra and chorus - amazing!

6.  Luke Kelly learns the song from Killen while staying in Newcastle in the early 1960s, but when he starts performing it, he uses a set of words from Australia instead of the Killen-Larner text (the 'returning with gold in great store' line originated in Australia).  The Aussie version was recorded in the 50s by Burl Ives, would have been easily accessible to Kelly, and is the most probable though not the only possible source (the Clancy Brothers actually say that TWR is an Australian song in an early performance for a Pete Seeger TV show that you can find on Youtube).

So there you go.