Thinking a little more on it, I'd hope it's included in beta 3/4, because that seems like a crucial thing to test before making it go launch official. Wouldn't want people changing their appearance only to find out some bug in the import process caused them to lose previous progress. Still would be nice to know if that would be our only chance though.
Also... if we change genders (which I suspect many people will be for male miqo'te), what happens to all the gender-specific gear like swimsuits? Do they get converted to the male version for us? Do we cross-dress? Or just have some now un-equippable items in the inventory?