Because we know that Maz Kanata is old and is seemingly being presented as an all-seeing sage sort of character (like Yoda), the question of who she might know from the earlier films came up. In particular, host Mindy Kaling asked Lupita Nyong'o whether she has a relationship with Yoda. JJ Abrams didn't let her answer:
"I do believe that Maz and Yoda at one point crossed paths, but of course due to the events of the past films, that's not something we'll see in this one."
So Yoda's not coming back as a force ghost then. Nyong'o also gave some insight into the mo-cap experience, revealing she did act alongside other cast members on set:
"I got to be on those sets, and feel them. It's mesmerizing. Audiences are going to have a very immersive experience."
And revealing both that the 360 camera around her freaked her out and that she's "still finding dots in things" from the two and a half hour preparation process of getting suited up for motion capture. Abrams, meanwhile was full of praise for her commitment to the role:
"She was remarkably tireless, willing to experiment with different versions of this character. It was an amazing thing to discover over the variations of Maz, what she sounds like, how she moves. It was something I've never done with an actor. She was willing, and game, and deeply committed to finding Maz's voice."