I saw an interview with someone who was outgoing, and there was some sly inference that the Inquisitor would have a much more active role moving forward than other previous Protagonists have had. I think the Cullen part was based on a string of other comments in conjunction with that. It wouldn't surprise me as much since they seem to like the character and enjoy building him more and more.
Honestly the DLC made it clear to me that the only character I'd for sure see in the next game is Dorian, but I imagine he'll at best be Morrigan-level from DAI. He's going to be too busy to party down with whatever Protagonist we get. ---