There's a difference for me between "extreme" and disgusting or degrading. I've known women who really enjoy oral sex and swallowing, and heard from others who enjoy the fantasy of large groups of men desiring them, and so it's not really that large a stretch to think a gangbang or group gokkun session is that unrealistic, as "extreme" as it may seem. On the other hand, titles like the 400 ml swallow you mention--and that I've watched (at least a couple)--strike me more as being humiliating and degrading, and I can't imagine the women taking part find any enjoyment in being forced to vomit up, and then re-drink, the large volume of cum that they've swallowed. And of course, then there are the Genki videos of women eating cockroaches and such (although admittedly, the idea of them having live eels wriggling around in their cunts is arousing). I can't imaging there's any redeeming satisfaction for the women in such situations, and frankly I don't really want to see it.
This brings me to one point I wanted to raise after watching Arisu Toyonaka in ASW249. This is one of the few Asfur films I've watched where I got to see the woman have an orgasm, and I must say that was incredibly refreshing. I don't understand Japanese, but I figure the conversation at the beginning of the film essentially moves to the woman's willingness to swallow cum, and in my own imagination perhaps, how much she says she enjoys it, or looks forward to trying it. But the scene where some guy moves in to perform cunnilingus, while another moves in to put his cock in her hand, and watching her try to continue her conversation with the director off-screen while she nears orgasm--that's gold in my book. She's got to be thinking about drinking cum, and the idea is making her excited enough to have an orgasm. Watching that one scene, even though it resulted not in a cum shot to the mouth, but rather her own orgasm, was incredibly arousing. I hope that Asfur incorporates more of that into their future films. Show the female participant having at least as much fun as the men.
Similarly with the Knights Visual creampie movies, the most exciting ones for me (although they're all pretty good) are the ones where the woman is masturbated with that little clit massager. It speaks to the woman's frame of mind where, when looking at all these guys who want to fuck her, it's nothing but arousing for her, and enough to make her cum. (That little clit massager, by the way, is as amazing as they say. It can easily bring my partner to multiple climaxes in less than a minute.)
So for me, my idea of "too extreme" or "too out there" really has much to do with whether I think the woman in the movie is having any fun, regardless of how scared of or disturbed by her own depravity (or that of the men surrounding her) she may be. That's why the Hawa series of films are great, because I can imaging the women thinking, "How did I get myself in this position of swallowing load after load of cum, but it's such a turn on I keep cumming." That combination of surprise and indulgence in depravity, and the subsequent enjoyment it brings to the woman, makes a mass gokkun movie so much more "epic" for me.