On the subject of kayfabe fading away, I don't think that's true, and once again the pro wrestling comparison comes in to play to prove my point. Everyone on earth knows pro wrestling is staged at this point, that the plots aren't real and are based out of a writer's room, and possibly influenced by backroom politics. But no one cares. The kayfabe is fun. Without it, there is no VTubing, it's just streaming. Look at Pippa; regardless of how much she opens up about her real personal life, it will always be through the lens of being a rabbit girl living in Phase World. Her father isn't "Dad", he's "Papakin."
The past Life stuff is also similar to pro wrestlers in that when they go to another company, even if they use the same name and visual gimmick, all the lore they built up in their previous company is reset. Their fans still follow them, going with the kayfabe for the fun of it, but always keeping the real backstage element in mind. The past life taboo was mostly for the fun of immersion, and to protect privacy when "past life" meant a non-VTuber presence. But reincarnations are happening so often, and usually from one VTuber persona to another, that the PL taboo is fading away. Basically there's a big difference between finding out the real name and identity of a VTuber because they were a cosplay model or something before joining a VTuber corpo vs. finding out they were just this other character previously.
Also, look at who disregards their kayfabe the most; primarily the Twitch VTubers, most of whom are e-girls trying the Amouranth coomerbait grift with an anime model, or who are otherwise openly narcissistic and just VTubing to be popular, evidenced by how often they share their real world face, political views, etc. on social media. The people who truly give a shit at least put in the effort to sell to their audience that on-screen character is who they actually are, even if they're not going full fantasy RP with it.
tl;Dr kayfabe never dies, it just evolves with the times.