All I know is that I'm sick of Y'shtola, Thancred, and the word "Allagans." I want them desperately to create a new heroine for their promo material and to give us another ancient high tech civilization with a less jarring color scheme than Allagans have, call it Lufenia, Gesthalian, Nifleheim, anything really.
I also would like to see a shuffling of our party members in order to create a team that has more meaningful interactions. In games like Dragon Age, your party members are not afraid to disagree with your actions and sometimes bicker/joke amongst themselves and it helps flesh them out as characters-the closest we've had to that in game come from our interactions with a certain trio in Elpis. The scions are pretty bland in comparison, other than Estinien and some of Alisae's more defining moments. I would like to see the spiritual successors to the trio appear in some way or form, maybe not as direct reincarnations but definitely feel free to draw from their distinctive personalities.
In terms of future settings-I will once again voice my opinion in support of a classic fantasy setting as opposed to something more niche "because X is located in this part of the world, X in FFXIV must draw inspiration from it." This trend is not sustainable in the long term and will result in either running out of ideas, or veering off into niches that do not appeal to the Final Fantasy audience. In short, send us to a kingdom, not another republic, and please avoid forcing in real-world locations/cultures without a strong enough link to the main plot.
(Also, I feel the need to remind people that New World/the Americas is not solely defined by tribal civilizations-it is entirely possible and more realistic to have European-style empires/kingdoms there in order to give a more Final Fantasy feel to the region, rather than an Indiana Jones one. To me at least, places like Mexico for example aren't defined solely by Aztec ruins-Mexico city has palaces, cathedrals, and various angelic statues that contribute to its makeup as well as its Aztec elements. Cuba is another place I would draw from if given the chance, with Havana's unique streets. I believe Lestallum in FFXV was based off it, actually.)
When it comes to the supernatural forces of the game, I would like for a new pair of gods to arise that inherit the will of Hydaelyn and Zodiark. This formed the basis for sequels to the two original Dissidia game: when Cosmos and Chaos both died, Materia and Spiritus were born of their enduring wills, but are distinct from their original counterparts. I believe this will serve to undo how we fell into the trap of basically "killing magic" again in Endwalker, as is the case in several Final Fantasy games like FFVI and FFXV.