If any woman should be on this album, it should be Beyoncé. I have reasons.
1. The album title alone is tribute to JAY Z, and it's seems like a feminist move for hip-hop, so Beyoncé would be perfect for this concept. Nicki has said on several occasions that she aspires to be the female equivalent to JAY Z in hip-hop.
2. Beyoncé is the most anticipated collaboration among Team Minaj. They've been craving a Beyoncé X Nicki Minaj track since the original 'Pink Friday' and Nicki has stated multiple times that she's aware of this.
I doubt it will be a pop girl, she is trying to be better perceived by the urban audience and a song with a pop girl would only make her look bad. A lot of people even bashed eminem for having collaborated with Rihanna, who makes pretty urban music. So I think it's between Rihanna, Beyoncé, or Jhene