According to a Reddit post, looks like the Zeta upgrade to the zodiac weapons will be easy. I can confirm that after doing one of the twelve steps yesterday, it should be smooth sailing to the end, unless there's a surprise thrown in there somewhere.

http://www.reddit.com/r/ffxiv/comments/2wyvdq/zodiac_weapon_zeta_will_only_take_you_a_week_of/