This is a really interesting thread by prokopetz on Tumblr:

Batman is kind of the odd one out among DC’s major heroes, because if you reverse Superman’s hero/villain dynamic you end up with “capitalism good, actually”, and if you reverse Wonder Woman’s hero/villain dynamic you end up with “patriarchy good, actually”, but if you reverse Batman’s hero/villain dynamic you end up with a weird homeless guy who dresses like a vaudeville performer fighting a billionaire with a vampire fetish, which is in fact an improvement.

Reply by dizzyhmuffin:

I feel like if you actually wanted to write this, you’d have to complete the gag by having Good Joker do all the same good deeds Batman does in canon, even when not directly Fighting Crime.™

Adopting a bunch of younger superheroes? Check. Trying to help all of his recurring enemies, occasionally including his gimmicky edgelord arch-nemesis, instead of solely beating them up as plan A? Check. Helping smaller-time criminals get jobs? Well, he’ll have to be more creative than “I hear Wayne Enterprises is hiring”, but if he’s clever enough to take on a supervillain who wants everyone to fear him and who has more money than God, he’ll think of something!

Also, the other thing that needs to be reversed is that Evil Bruce will be obsessed with everyone to recognize his artistic/comedic/edgelord genius, whereas Good Joker is going to be straight-facing the most ridiculous nonsense and his shtick depends on nobody being entirely sure if he’s messing with them.

Reply by prokopetz:

I think the best way to approach the last one would be to swap the ethos, but not the subject matter. Like, Canon Batman is like “fear is my weapon” and Canon Joker is like “comedy is my art”, so Evil Batman becomes “fear is my art” and Good Joker becomes “comedy is my weapon”.

Now, I know one’s initial reaction might be “isn’t the ‘fear is my art’ guy just the Scarecrow?”, but the important distinction is that for Evil Batman, being an asshole billionaire isn’t necessarily a put-on. Let’s suppose Evil Batman fancies himself an Artist of Fear™, but he’s incredibly pretentious about it while at the same time having a very shallow understanding of how fear actually operates. Like, picture Patrick Bateman levels of shallow pretension and you’ll have have roughly the right idea – and I’m not just picking Bateman as my example because both Bateman and Batman have been played by Christian Bale, though it certainly doesn’t hurt! He only thinks he’s ahead of the curve because he’s playing with a stacked deck.

Meanwhile, Good Joker’s “comedy is my weapon” shtick forms a natural counterpart by working to demonstrate what laughable horseshit Evil Batman’s “I am the night” routine really is. He’s all about confronting the banality of evil, going in against villains who carefully cultivate the image of grand, romantic antiheroes and publicly exposing them as absurd little men with pie on their faces. Canon Joker’s comedy sucks because he doesn’t take anything seriously, but for Good Joker, nothing is more serious than comedy; like all really effective comedians, his best material comes from a place of white-hot anger at the systemic injustice that guys like Evil Batman represent. The text is “ha ha, I’m a silly clown”, but the subtext is “how dare you”.

I may have put entirely too much thought into this.

Reply from kradeiz:

Lot of people in the notes bringing up Earth-3 but that's not quite the same since that's a universe where all the heroes and villains are swapped. Here it's just Batman and Joker, which presents some new possibilities.

Like what's Batman's relationship with the other rogues? Does he get along with any of them or do they just tolerate him bc he's loaded? Is he still dating Catwoman and if so what does that look like now?

Same thing with the Joker and other heroes. Having Robins still makes sense, especially Dick since a circus orphan fits the clown theme so well you'd think that was the canon. But what about the rest of the League? They have their fair share of wisecrackers but how do they bounce off a guy whose arsenal is comedy?

Personally I like the idea of him hitting it off with Martian Manhunter. J'onn is woefully underused in a lot of media and his quiet, gentle nature makes him the perfect straight man for Joker's off-the-wall personality.

It’d also be funny if we still didn’t know what Joker's backstory is. We get hints once and awhile (some of them contradictory) but just enough to give us a vague idea. And it'd be fun to see people in-universe drawing their own conclusions.