These are all good points. Just to prove I am a legitimate creator, this is the comic I am currently working on:
This one is on The Duck and Comic Fury because the format works better. I also have this one on webtoons:
They have similar themes but the second isn't a superhero comic, it's a sci-fi fantasy.
What I am proposing wouldn't necessarily have to be everyone working on each other's comic. Technically, by law you have a copyright to your the moment you create it. However, I can see how someone could have a fear of someone else swiping their stuff.
It could also be done simply by an agreement to cross promote our stuff and to have a single central hub we drive everyone to. There you would see all superhero comics that are participating. It would raise everyone's visibility. I love superhero comics, but they are really tough to find on these websites as anime is the dominant force these days; but that doesn't mean there isn't an audience for what we do. We need to find a way to make it easier for our readers to find us. Like I said, it would be a virtual comic book store dedicated to superhero content. We could even make the front page like a comic book rack with all of our latest covers on it.
With that being said, crossovers could help a lot to generate interest but I don't think they are a must.