Sayu did approach Kson about joining Vsj early on, but while Kson was sympathetic, said the some of the other members weren't sure about Sayu yet. This was still when she would tangent into venting about her old job and I think that might have been the issue. The other issue is that at the time, she didn't really have a strong connection to anyone at Vsj and viewers were just trying to meme it into existence. While I still think she would jive better with the other members of PhaseConnect, Vsj isn't completely out of the realm of possibility.

A month or so ago, Sakana revealed that PC is already in preliminary talks with three new Invaders. If Sayu is going to end up with PC, she would have been one of those three. I think PC has a few already locked in, but wants to round off the next wave with a few more and that's who auditions for new Invaders was opened. I'm not really a fan of Genshin Impact, but I do try and catch Hag Emblem or any other collab she's in.

Some people also suggested Idol, but they just debuted their "Encore" gen, so I doubt they're ready for another similar group so soon.