I don’t think it’s crazy to assume that 10 movies are planned. Often plans that are that far in advanced don’t play out as planned.
It sounds like Yonkou is just freaking out over reading the new chapter releasing this Sunday, which spoilers for should be leaking soon.
Which I’m guessing the plot takes some sorta of turn that’ll show that the series could last way longer than we initially expected.
People are questioning him in the comments about his claims that “MHA has a loooooong way to go”, which I think triggered his “10 films” post. Which is him basically trying to say “TOHO, at the very least, WANTS to make 10 movies, so that shows that the series could potentially run very long”.
Also, we’ve been getting a lot of any post-manga movies for big franchises in the 2010s and probably in the 2020s(Naruto, Dragon Ball, City Hunter, YuGiOh). I doubt Heroes Rising is the last planned movie, and I would think it’s crazy that the production Committee would want to continue making movies as long as they continue making money, even after the manga ends.