I don't think they'd ever collaborate, at least not in the sense of a vocal duet. Their styles are entirely different. If they did, it would probably be yet another promotional gimmick (the reverse of the previous one) on the part of their record companies. Although they may get along, I doubt either one of them would take it upon themselves to initiate an unnecessary collaboration.

As for that MS interview, it was very cute! Because Ayu lived in New York before her debut, and Hikki is from New York, the two of them were bonding, and talking about different parts of the city. Later, Hikki said she sometimes sings Ayu's songs at karaoke.