ok so if i was in charge of ace attorney here is the aa7 i would make:
full remake. no announced returning characters from previous games.
prologue. the game opens with that insane legal academy from aa5 where students are either defense attorneys, judges, or prosecutors. we see a pair of twins (identical, yet different genders) and their childhood friend.
twin A is a prosecutor. twin B is a defense attorney. childhood friend C is a judge.
we see a cutscene of these three at graduation, affirming their eternal friendship, despite their paths separating, and vowing to uphold justice or whatever. possibly they hint at some tragic backstory.
the game then offers you a choice a la pokemon: are you a defense attorney, or a prosecutor? you select one of the twins. you then enter one of two story paths.
ideally i think each of these paths will have 3 cases and ideally they will be three separate cases. the twins will not see each other during this part of the game, and will only hear of each other's exploits in passing. these 3 cases would be typical aa-style cases with investigation and courtroom portions, even for the prosecutors, which is the one thing i think was missing in aai and aai2.
these cases will initially seem to be three separate crimes, but will be connected somehow to an underlying legal conspiracy of some kind that you will gradually start to uncover.
C will be the judge for all 6 cases.
when you have finished one path, you will be on the cusp of discovering some important information, and the game will prompt you to play the other.
when you have completed both paths, you will unlock a massive final case, where you will have to unravel the conspiracy and discover what evil soul is at the heart of it. spoiler alert, it will be your childhood friend the judge, who is presiding over the case.
in my dreams, you get to decide who you play this case as, and it unfolds differently depending on whether you play as A or B. I think it would be cool if the twin you aren't playing as has a different motivation for opposing you depending on which twin you, the player, choose to be.
for example--maybe if you play the case as prosecutor, your twin will do a bad job defending their client because they are in love with C and don't want them to go to jail, and you have to convince them to Believe In Justice. but if you play as defense attorney, your twin will prosecute your innocent client relentlessly because they have been fed false information that you are in the legal conspiracy, and you have to convince them to Believe In You.
i know in my heart aa7 will open with lamiroir being murdered before trucy and apollo find out she's their mom, thereby giving capcom a chance to give apollo a fourth tragic backstory. but i can dream.