I'll sum the 50 pages of 3 threads up for you:
Look at this guy's bow. Okay, now I'll re-enact the progression for you. Pretend after every line I'm using a different one of those voices people use to imitate eachother.
Oh, my god. What's on his bow?!
That looks like a harp!
It's not a harp!
I'm so glad we're going to be able to play BARCHER!
F**K BARCHER!
I HATE YOSHI-P BECAUSE WE'RE GETTING BARCHER.
I, FOR ONE, LOVE THE IDEA THAT WE'RE GETTING BARCHER!
Guys, are we sure it's a bow-harp?
I CAN'T WAIT TO PLAY BARCHER.
I DIDN'T LEVEL ARCHER TO BUFF.
Hail! I am a Community rep and I can confirm that the bow transforms.
YAAAAAAAYYYYY
NUUUUUUUU
Transforms into wh-
BARCHERRRRRR!!!!
Empirical Evidence
It looks like a lyre (a type of harp). If you fold it up, it looks even MORE like a lyre. It could be a crossbow, but even the symbol carved into the bow and shape of the outer border are very akin to styles used for musical instruments. Particularly the flourish on the handle, you'd expect to see that on a violin.
Square-Enix supposedly released somewhere what jobs would be coming first - and ARC and BRD are the only two left over after you match up all the obvious ones. Combine this with the above? Barcher. Probably. (By probably, I mean maybe.)
It could still be a crossbow after transformation. But come on, what does it look like to you? Obviously it doesn't transform into a pez dispenser.
EDIT: Bonus fact - Archer turning into Ranger would be redundant. They're the same job. Combine this with what I said on the first page about Rangers not being "ranged attackers" but people who "range over an area" and ARC >> RNG sounds just as silly, if not sillier, than barcher.