The shooting script seems to think he's alive and well and employed and living with Jayne's mother. Maybe that's why they cut those lines from the aired episode.

I always thought Jayne paradoxically had the most normal upbringing of any of them and the whole family is pretty much "Cobbs first and the devil take the hindmost." The kind of close-knit, loving family that robs banks together or something.

And I was hoping that Jayne was a replicant with implanted memories of family and home.

You people are Not Helping.

OMG! He's a cylon!

Me, if it's not on-screen canon, I don't have a problem with it. Unfilmed script dialogue argues as to the intent of the writer(s) but it was held back, perhaps to be contradicted later depending on plot needs, et cetera.

What Theo said

It's perfectly valid to ignore the supertext in favor of actual canonical content, as not everyone has access to it. I mean, unless the supertext involves a hell of a lot of groping in the case of the Due South gag reel, but I think that goes without saying.

I would almost consider giving Ron Moore a pass on the whole Jimi Hendrix thing if Jayne Cobb turned out to be the last Cylon.

Imagine if Starbuck leads everyone to Earth, and instead of being modern early 21st century Earth in the Galactica 1980 tradition, it's 25th century Earth-That-Was!