Welp, the actor that played Lem Lemoncloak onthe last episode just "confirmed" on the social media that she's really coming to the show, even though they said a long time they wouldn't make it to the tv show.
Regarding Arya, I've seen other theories around that say the Waif is actually Arya herself, in a twisted Fight Club dissociation process, part of a process that would make her finally cut ties with her former self and finally becoming "no one", a faceless man.
This would explain somehow why would a blind girl get beaten in the middle of the day with a wooden stick and no one would give a fuck. Also there's a glimpse of a girl in the last episode, dressed exactly as she was during the play day, which is confusing a lot of people.
I kinda like this theory better, personally.