Preemptively, the Butler and Housemaid attire from the 7-11 promotional event, whenever that arrives to players in the US and EU.
The Bunny/Chief Bunny, Thavnairian, and Expeditioners sets. (I would really particularly love to see the female-only Expeditioner's/Ramie chestpiece unlocked for male characters, and vice-versa for female characters.)
The Summer Dress being unlocked for male characters (especially since a version of it does appear on a certain male Highlander at a certain point during a certain optional questline!!!)
The Oasis and Riviera gear from the Gold Saucer for both sides of the equation.
Additionally, I was a huge fan of a unisex, glamour-able version of the female variant on the Boarskin Skirt being added in 3.2. There are a lot of pieces of gear that differ greatly between male and female characters, and making both variants available to both genders is a trend I approve of. Give male characters the option to wear the fishnets from the female Evenstar set, the skirt from the Acolyte's and Foestriker's, the skirt/stockings from the various female versions of the bottoms/coatee set, and the shorts/stockings on Arachne Culottes, and the more open-chested and frilly versions of coatees and bliauds. And in return, let female characters have the pants from the bottoms/coatee and the option to close up the chest on coatees and bliauds (and not expose their stomach with Dragoon artifact gear!) The short-pants version of the Arachne Culottes of healing/casting, the striped trousers from the male Evenstar set, and the various skirts with pants/stockings underneath would also be a good thing to give to female characters.
And though it is not gear, I'd really love to see more hairstyles made unisex, with minor or no alterations. The Lightning/Snow hairstyles, the player-designed contest winners, the dreadlocks that are currently only female-exclusive... I'd like to see more things like how female Highlanders get a lot of male Midlander/Elezen styles but extended to more characters. (The shaved head hairstyle that only female Elezen and male Lalafells get would be a good one to add for more female characters, though I can see why Au Ra and Miqo'te are unlikely to ever get it.) Making it possible to give the Minfilia hairstyle to male characters would also be swell. (As would letting them wear her clothes- and giving the opposite opportunity to female characters who want to dress up like Cid! I've seen a lot more players of female characters interested in that set than players of male characters.)