What I would want is a contemporary version of the essence of Final Fantasy VI. The story takes place in a large, diverse city that's a mix of Victorian gothic and sci-fi (or some interesting mix of two genre aesthetics). You have a diverse cast of characters with interesting backstories that intersect in different ways with each other, sometimes even in contentious ways. Of course one of the FFVI ideas is a game set in two phases, whether that means the city is fundamentally transformed halfway through or you venture out of the city to the wildness or some foreign place after spending 20 hours getting to know the city (or more, it is a JRPG).
A lot of the superficial trappings and details don't matter other than it needs to feel like Final Fantasy. I think you captured the spirit with a moogle as a mentor, it's that sort of on the face of it silliness that really works in the series. Final Fantasy XV is somewhere between a decent game and a very good game, but in a lot of ways it just doesn't feel like a Final Fantasy game. Summons are very reduced, spells are grenades, the only race is humans (basically) - it just feels kind of bland with a veneer of Final Fantasy shining through. So it's important to get back to that interesting mix. I love having a moogle in my party, or a lion dog, or a frog thing, or a blue lion that walks like a human, or a furry...okay you get the picture.
Honestly though combat is the most important thing. Sure "I" want the story and characters more, but the game needs to be fun. I love turn based games but it needs to be action-oriented. At the same time it needs to have strategy and a variety of ways to approach a fight. I think a modified version of what kingdom hearts Birth By Sleep/Dream Drop Distance did could work. You have a selection of commands selected that you can quickly cycle through as well as basic attack commands you can do without needing to look through the menu, but you also need the ability to use a spell or something that isn't in your preselected "deck." Also, every character should have one thing they do that no other character can do, although improving relationships and leveling up characters (kind of like Persona) will allow you to share more basic class features amongst characters.
So the main character might be a balanced fighter with good physical attacks, okay magic attacks and the special ability to meld attacks. Maybe linking a physical attack ability with the Fire spell results in a Flame Sword attack, with the ability to eventually link three or four attacks and establish these melded attacks as a single command in your deck. Another character might specialize in tools where they use items and it creates a special attack - for instance using a dagger might result in a Blade Barrage attack that can cause bleeding, and while other characters can't use the Tool command maybe some specific attacks can be learned like Blade Barrage. You choose the different commands each player has and the computer will mostly rely on these although not exclusively. Also, I think it's borderline necessary to have some system where you level gear, weapons, summons, or something and by doing so not only are you acquiring new abilities for/from the thing but it or you are getting stronger. FFVII, FFIX, FFX, Kingdom Hearts Birth By Sleep, Persona 4/5, there are a few examples of game systems outside of just leveling your character to consider when playing.
Another important thing to consider is the environment. If you are fighting in the streets during a rainstorm and use fire attacks the damage will be reduced but it can create mist that can obscure the battlefield (and reduce the enemies chances of hitting you). Conversely if you use a thunder attack it will do more damage but will also do some damage to you. Any ways to incorporate the environment whether directly through changing the way the combat system responds like above or in creating more dynamic encounters such as fighting in an area with moving objects that need to be accounted for by dodging or even smartly used as cover, that's a big part of it too.
This is a very, very, very shallow idea of what I would like. Truthfully unless you are literally just copying whole swathes of game design from other stuff it takes a lot of words to accurately describe the ins and outs of gameplay, story, lore, characters, etc. I will say there are two more things I really would want:
The secret puzzle/platformer dungeon in FFXV is a fantastic but pretty janky piece of wonderful game design. Dungeons in FFXVI need to have unique and interesting ideas in them, and there needs to be a more polished and balanced version of the secret FFXV dungeon.
Gilgamesh needs to be in the game, he needs to be a fight whether optional or part of the story, and he needs to be awesome. In my dream version of FFXVI you fight him several times, the first time he's wagering one of his swords (an iconic FF weapon) for you Sword. After the first defeat he comes back and doubles down, offering another sword for yours plus what he's lost. I'd say you fight him three times, with a fourth optional time being very hard and him revealing what he gave you were fakes but he will give you the ultimate weapon if you can beat him when he really tries. Maybe 3 fights and one optional fight is too repetitive and can be scaled down to one fight and one optional fight. This needs to happen Square Enix.