On top of that, think about what is left to explore in the plot. There isn't so much more than the third floor and the great grandfather. I think the climax is due, wouldn't want to see it become uninspired.
I feel like every "game" Kate has been doing in the Children's wings could be expanded to the 2nd floor but well. I agree that it'll be half as short at best, and I agree it'll be slightly uninspired if the plot goes there. I just thought it would be interesting if Kate has to adapt to a new environment and get an invitation, where after she can fool the process, she has to start from zero allies.
And again, seeing how she once masked Anthony to act as Christopher to console Barbara through the seizure, I think she could do a similar thing with Emilyko to make her appear as a "unified" Kate while she hides.
Alas, the cat is out of the bag with the Anthony monologue imo. The reason there isn't "much left" to explore is because the dumping was very compact (unlike previously; where it felt like things were being dripped little by little while Kate's focus were always other worries in the social game of the house.) We suddenly have Joseph into becoming an actor in such a short time where Anthony was built up as one for a good while, because we haven't seen much of the upper floors in the same way we see the Children's wing.
