how would you have done Joker 2 to ensure another billion hit?
All they had to do was something along lines of the 1st film .. an 'Unbreakable' style deconstruction of the Joker mythos, and something that would excite audiences and pay off some expectations from 1st film..
I can probably come up with a premise just off top of head on which to blow *gasp* 200m! that would have a decent chance at being a billion hit and keep everyone happy (audiences, shareholders, studio bosses, even some critics)
-Start off with opening trial with Harvey Dent etc, Arthur sent to Arkham for life.
-Flash forward 15y to late 1990s we see Arthur (who is now like 50 bc hes prob only supposed to be 35 in J1) escapes in some big mass jail break like in Batman Begins - (we briefly see likes of Penguin, TwoFace, Riddler, etc), by now 'joker' has totally taken over Arthur so he's like the traditional Joker (the proper genuine one). There's the romance with HQ (GaGa) but no musicals beyond like one fantasy set piece.
-then it becomes something of a crime thriller for bulk of movie, jokers ascent to crimelord abit like 'The Dark Knight' but from Jokers POV ultimately terrorising Gotham - 'year one' Batman would be in shadows, vague urban myth, not really seen until the confrontation finale, where 'Arthur' would come back briefly when he realises its Bruce. Batman would be an unknown guy in fact maybe never even see his face, and would be a very closely guarded spoiler not revealed in any trailers, publicity etc to keep it a surprise.
-ends with something like last shot of TDK but with Joker and HQ in the Jokermobile (like that scene in Suicide Squad)
Therefore couldve been like a mirror to the Nolan trilogy. J1 would be (retroactively) like 'Joker Begins', J2 'The Dark Joker', (and a potential J3 could be 'Joker Rises') as well as continuing with the Scorsese vibe (Goodfellas/Casino, Gangs of NY/Departed)