I mean, it only makes sense if you think about it. So far, the only big streaming service that has been avoided is xCloud, and by extension Game Pass. So it is obvious it is going to come to consoles. With that, Ubisoft associating themselves with the most popular service on console right now also makes sense, since it would be a partnership beneficial for both Microsoft and Ubisoft. They would both be bolstering their subscription numbers.
I think there is a chance it could be and add-on for $5/month more if you already have Game Pass Ultimate.