Forks are similar to citations in a way. It's not the same, there are many differences, but there are some similarities in my opinion. By the way, wouldn't it be great to be able to contribute to papers, and their assets (figures, code, equations) ? I don't know how a system like that might work in practice, it must be non trivial to govern, like any other sizable community - but I can see how it could work.
Does science really need to pay for recognition and prestige today ? It used to be the these journals allowed more people to have access to quality research, now it restricts them. Non free journals are dead a parellel universe Nietzsche might write.