Yeah, I'm all for at least discussing new things, we're so much in the dark that we might as well entertain the more out there possibilities. I've been wrong about everything I've been predicting for #5, so I'm not going to pretend like I've got a good grasp on what the hell is going on haha.
If something like a Hollow Knight character were to happen, I think it'd have a lot to do with Nintendo pushing it over other indie titles, they've done a lot to promote Silksong by bringing demos to conventions as well as showcasing it during the E3 Treehouse (and clearly having a lot of inside knowledge of it beyond what they showcased), so I get the feeling that they have a lot of respect for the series. That might just be a NoA/NoE thing though, and it's obviously going to be the higher ups in Japan who are the ones suggesting characters to Sakurai, but I suppose it's not impossible. It's also worth noting that it seems like the original game did decent in Japan, or at least well enough that the physical Collector's Edition was released there.