Generally speaking, all the major instances are federated with all the other major instances.
The differences are the super tiny instances (which are generally effectively zero traffic) and the controversial instances (mostly tankies). Said controversial instances don’t want to advertise that nobody can stand them and the rest of the instances don’t want to deal with the bullshit from bringing it up again.
I think it would be a nice novelty to visualize this. But I don’t think there would be much actionable information coming out of it and , because this is The Internet, it will likely lead to harassment and brigading.