What exactly did Arya learn backstage? The guy who plays Joffrey has two warts on his junk, which we were shown in a nice bit of meta-nudity. Bianca wants more lines, too. And Lady Crane, the performer Arya has been assigned to kill, seems kind-hearted and chill. She's drinking rum backstage, flirting with the other performers, and she's played by the excellent Australian actress Essie Davis from The Babadook, so she'll likely stick around for a bit. We'll also probably get a few more moments with Izembaro, the cranky leader of the theater troupe, played by Richard E. Grant.
There are a few directions this story could go in. Arya could carry out the orders of the Faceless Men and kill Lady Crane by poisoning her rum. Or, if she was charmed by the performance she saw, she could end up joining the troupe, and the next few seasons of Game of Thrones would take us even deeper into the underbelly of the comedy world in Westeros and Essos. Stranger things, like time travel, have happened. As Jaqen H'ghar, tells Arya in the episode, "A girl must decide if she wants to serve the Many-Faced God." He could've just as easily added, "A girl must decide if she wants to sign up for improv classes."