A bit late to the discussion ? ^^
It was already discussed a lot, and in fact the
chemist would have been a good guess.
However, on a more recent interview (can't find the link, will update if I find it again, maybe it was in the live letter at E3), Yoshida announced that the gunner class would be a support, the very first support class in the game (as opposed to the bard which is a dps with support abilities), and that by that time there would be more supports coming. That led people think more about FFXI corsair or FFX-2 blue mage
edit :
FFT's machinist (engineer) is also a good guess, maybe ?