I'm nearing the end of 16 this week and I find the game fantastic but with a good chunk of flaws. All things FF17 could easily fix.
There's still so many ways they can approach how to make the franchise super relevant like it once was. Everyone has a theory . "Make it turn based again." "Go back to FF12s Ivalice." "Do this do that"
If I were them I'd invest in 3 new franchises but tell each team whoever makes the best game will get the chance to then do FF17 with their game as a base. Let them take creative risks on a smaller budget scale. Take a FF16 budget and split it 3 ways. This could lead to the spark being found.
I personally would like to see them make a FF where I can make my own lead character like in FF15s character creator. Then learn from games like BG3 on creative quests with weight to them. Throw in combat that melds something like sea of stars with FF7 remake, and for the love of god give us a hard mode from the jump. Give us visually changing gear like FF stranger of paradise. Lastly, learn that the game story, world, and lore cannot keep being dumped into books to read in game. Make it work straight up. Also, yes, people like to play as other characters from the team.
That's just one set of ideas. I think a team like monolith with SE money would bring the franchise back to expectations for fans and the money guys .