Mmm. I understand where you're coming from in regards to the culture there, but that culture doesn't really extend to this stuff. The only thing in Japan you can't talk about to anyone except your best, BEST friends and family is Politics. Talking about your sexuality to your audience is only frowned upon if you know your audience doesn't want to hear it.
Gundou Mirei, Sara Hoshikawa, Sukoya Kana, Shirayuki Tomoe, Suzuka Utako, Rindou Mikoto, Melissa Kinrenka, and Hayase Sou are just a handful of V-Tubers who've discussed sexual/LGBT experiences openly to their audience. Astel Leda and Kageyama Shien of Holostars have, too.
In regards to Okayu and Korone, I think it's more likely that they AREN'T fucking, and they aren't dating because, if profiles are to be believed, Okayu is 23 and Korone is 36 - the age difference probably being a bigger personal barricade for them than social norms. This is especially true when Korone is clearly from Kansai which is the only prefecture where being gay IS legally accepted.
For some reason, too, male otaku retards don't view 'yuri' or the notion of lesbianism as a threat to their chances of maintaining a parasocial relationship with them. Flare and Noel being handsy and having cute stories doesn't really cross the threshold of breaking immersion. Immersion gets broken and their images as idols in jeopardy when the relationship crosses the 2D barrier; and it becomes clear that no amount of simpbucks will ever get you the big titted knight because she's taken by another person.
You can't convince me that every member of Hololive is a complete wallflower who has no stories of clubbing, relationships, sex, funny bullshit that's happened whilst they were drunk with friends, etc. They don't talk about it because that's not what they do. They have an image to uphold, and no matter how intense their relationship may appear compared to others Holomen, it's still sort of camouflaged in a vast rainforest of kayfabe and unable to break out into the sunlight.
If you want to believe it's legitimate then that's totally fine in my book, but there's no reason to 'just assume it's real than justifying that it isn't' when there's no real reason to believe it is. Most people here don't care much either way.