Wonder Woman: “My invisible jet had a huge carbon footprint. For the sake of the environment, I replaced it with this Invisible Tesla.”
Aquaman: “Sure, Atlantis is okay. But it’s no Portland and you can’t get authentic avocado toast, tostados or java.”
Batman: “I am going to have to unfollow The Joker. I’m so sick of his stupid puns and dad jokes. Lame!”
Superman: “Hey Boomer… ‘I’m really trying to focus on journalism and photography at the moment!”
Pretty much all of them, but language-wise closest to Superman:
"Truth and Justice? False social constructs, words to keep people in place and believe that the system works, and thus support it. I’m getting out of this false system, and help everyone work towards a more equal society.
Super-villains aren’t the problem, alien invasions aren’t the problem, the problem is society itself!"
We already know what happens to Captain America. He turns into Nomad.
In Captain America #180 (December 1974) Rogers becomes disillusioned with the United States government, when he discovers that a high ranking government official (heavily hinted to be the then President of the United States Richard Nixon) is the leader of the terrorist organization known as the Secret Empire.
Rogers then decides to abandon his Captain America identity, feeling that he cannot continue to serve America after this latest discovery has shattered his faith in the nation’s status. However, a confrontation with Hawkeye (disguised as the Golden Archer) forces Rogers to realize that he cannot abandon a life of heroism, and he subsequently takes on the name “Nomad” (as it means “man without a country”) adopting a new dark blue and yellow uniform with no patriotic markings on it at all.
Ugh. 
And the less said about hipster Spider-Man, the better.
They’d have to stop flying because their fedoras would keep blowing off.
Teslas are way too common for hipsters.
Ahem.
Oooh.
More.
Iron Man: I have replaced 80% of the iron with more environmentally friendly post-consumer aluminum fibres. This also reduces the weight and increases efficiency.
Plastic Man: Yeah? Less than 10% of American plastics are recycled. I am leading a consumer campaign researching how to clean the vast collections of plastic refuse in parts of the world’s oceans.
Matter-Eater Lad: I was safely disposing of radioactive waste before it was cool.
Wolverine would need an adamantium wheel to keep his claws from shredding it, and beer in his water bottle.
Reed Richards’ cheeks would hold a whole bag of seeds.
Oh, wait–hipsters. Never mind.
This brings to mind when superhero characters in the late 60s would adapt hippie styles of clothing and patois: vertical-striped pants, pimp shoes, flowers in their hair, and phrases such as “Far out” and “You dig?” Then, the good old Conservation Christian superheroes would straighten them out, lead them to see the error of their ways, and they’d go back to being normal.
One of my favorite “What If” scenarios (before Marvel made it a thing) had Superman deciding if he duplicated himself, he’d be twice as smart and could devote more brain power to eliminating crime. So, he made a machine that split him into Superman Red and Superman Blue. The two Supermen collaborated on a satellite system that would suck all the evil out of Earth’s inhabitants, even invading aliens. There were a couple of panels of Braniac 5 leading a fleet of space ships, only to get bathed in the light of the Ray of Goodness. Brainiac 5 then smiles and says, “Why should we conquer Earth? It’s such a peaceful and serene planet. Let’s go back home.”
What are the best examples of sixties style heroes? Though Shaggy never reformed AFAIK, the era is before my time.
The DC version of What if…? were published as “Imaginary Stories.”
You know, to differentiate them from the strict historical accuracy of the regular Superman comics,
I think the ultimate 60s superhero was Brother Power the Geek
Shortly after his creation, Brother Power was kidnapped by the “Psychedelic Circus”. The freaks in the Freakshow at the “Psychedelic Circus” were all based on the styles of “Big Daddy” Ed Roth and Harvey Kurtzman, both of whom were good friends of Simon. After escaping, he was fixed up and given a face by another hippie named Cindy, and attempted to run for the United States Congress. His misadventures with the establishment led to finding work and encouraging other hippies to do so, eventually getting hired by the J.P. Acme Corporation just as it was taken over by the wicked Lord Sliderule. Brother Power’s ingenuity still made the assembly line run more efficiently. Brother Power was last seen being shot into space on orders from Governor Ronald Reagan, after trying to prevent the sabotage of a rocket launch by Hound Dawg and his gang, knowing it would be blamed on hippies.
Hipster Superman walks into an empty bar and duplicates himself…
“Let’s get out of here, this place is full of hipsters!”