4chan definitely doesn't change the industry that much, the western fandom would be fairly different but we aren't really a major audience and it wouldn't be so different as to truly change spending habits. the big sellers over here would still be toonami/adult swim nostalgia and blockbuster shonen and everything else would be pretty niche and not really make any impact on the japanese industry side of things. people would post differently and maybe the way anime gets distributed would be a little different but i'm pretty sure nothing major would change there

2chan is a different story, but not one i'm super qualified to talk about. 2chan makes up (or at least made) a huge percentage of the hardcore otaku audience who are the ones buying figures and discs. now most people there would probably still be anime fans without 2chan, and they'd find other forums to talk anime with people, but if 2chan never existed there would probably be some major changes in how the industry worked. couldn't say exactly what though