In an interview Yoshi said that they're making each large zone into many separate zones so they can go about using different textures and whatnot. To my knowledge they aren't planning seasons (as far as what they've said). They do kind of do it with holidays (cherry blossoms, snow etc.) but that's it. They're planning on making weather an important thing though and also when a Company summons a primal the weather all over Eorzea will change to correspond to that element.

I think with all of the changed zones it could become a coding nightmare. FFXI had seasons and all it did was change the frequency of weather patterns. I could see this happening again along with more widespread seasonal props.

However, keep in mind Eorzea is just an island on the planet, it could be located on the equator and never experience seasons. That could lead to an expansion down the line to an unlocked continent having seasons that they could code from the ground up.