I think it likely a nonsense word added for rythym and nothing more. I believe the term "bra" used as a replacement for "bro" (which I associate with Hawaiian surfer slang) didn't yet exist in 1967 and even if it did I doubt ol' Macca would've known it.
The title came from a friend of Paul's named Jimmy Scott, a musician who was either Nigerian or Jamaican (I cannot find out which). I have heard that Obladi Oblada is Nigerian for "life goes on" but I cannot confirm that, either. Anyway, Paul said in an interview that he used to ask Jimmy how things were going and Jimmy answered "Obladi oblada, life goes on, bra." I agree that "bra" is probably a version of "bro". Or maybe that is just how an Englishmen heard "bro" in a Jamaican or Nigerian accent.
I agree that "Bra" is probably "Bro" (short for "brother")
Remember that sometimes the vowels are many times unclear to foreigners because of the "schwa" prevalent in the English language. Many vowels are pronounced "uh" when they are unaccented. You could google this to understand it clearer.
"Bro" - "Bra", it is probably the same when pronounced. (However, I wonder why they chose to write "Bra" in the lyrics instead of "Bro".)
I tried to google "bra" but forgot why once I started veiwing the Victoria's Secret models...
I think the reason Paul kept bra instead of bro is that it fits the rhythm and tone of the song. "Obla-di obla-da, life goes on" are three phrases of three syllables each, each ending with an upward lilt. Bra is a quicker sound than bro and ends with a clipped, upward sound, while bro is a slightly longer sound and has a flatter tone. The upbeat sense of the song is maintained better the way it is than it would be with bro. Also, the vowel sound in "bra" is the same as "da" "la" and "on" (as in la-la la-la, life goes on). The Beatles didn't just write and play music. They painted with the lyrics and melodies; like Da-da-ists, they used the sounds even when the words were nonsense. Bra fits the "color", "texture" and "shape" of the song better than bro would.
The Irish bràth (forward accent, not sure how to do them) however is a different sound, prounced as the 'aw' in law.
Is there any way to confirm the meaning of Obladi oblada, I'm intrigued by this thread!
Nigerian musician/singer Jimmy Scott later claimed that the phrase "Ob-La-Di, Ob-La-Da" was originally his; Scott sued McCartney for compensation for using the phrase in the lyrics and as the title of the song. According to McCartney, "Ob-La-Di, Ob-La-Da" merely was a common saying of the Yoruba tribe, and Scott had simply taught the saying to McCartney. It reportedly means "Life goes on", words which are also heard in the song. The case was settled out of court.
However, I am not able to post the URL (too new here). I found another source (reliability also unknown) in Geocities that confirms the origin of the phrase as from the Yoruba tribe of Nigeria, meaning "life goes on".
And that most revered of all Internet sources, Wikipedia, also says so.
I think you all should consider that McCartney put a Swedish word into the lyrics which fits the context but means something completely different in English. The meaning of "bra" in Swedish is: "good", "well".