Reading some of the responses, it's heartening to see the number of people taking this seriously, some repeating a line that's something like "cosplay yes, touch no", similar to the "cosplay is not consent" saying around here. It seems some have also suggested that photographers should have to sign up for special armbands or lanyards at Comiket so that if they do something skeevy they can be identified. That does seem useful, especially given the number of congoers that seem to wear facemasks to conceal their identity (which can absolutely be done for legitimate reasons and I don't think is a bad thing inherently, but can just as easily be to, well, avoid being caught doing skeevy shit).
As an American congoer, who is used to just saying "hey, can I get a pic?" if I see someone in a cool costume and if they say yes I do so, and if no, go on my way, that seems really odd. But the whole idea of cosplayers gathering in a square with the intention of letting a literal wall of photographers take pictures of them with little to no real communication is completely foreign to me. If that sort of thing was the norm here, I'd absolutely be for it.
As is, I'd personally suggest Japanese cosplayers begin to ask photographers for individual photo sessions and outside of that ask people to individually ask them, rather than throngs of people encroaching upon them. But maybe that's me being culturally insensitive and they can figure out methods like the aforementioned armband one themselves.
Sidenote, fuck the guy in the responses who posted a gif of a baby panda rolling around. It seems the cosplayer in question was a Chinese person, so you know that was just a mixed misogynist-xenophobic response to a serious event.