Here are his exact words from the translation: "We decided which fighters to include when we started planning, so we couldn't add characters from titles like Xenoblade Chronicles 2, which was announced after planning had started."
My original read on that statement was that Rex was being heavily implied as DLC and that Sakurai was referring to the base roster. However, considering how long it takes to develop characters, stages, and music, I can't fully believe Sakurai's when he says that they haven't started development on the DLC yet. That's why I was thinking earlier that Granblue might be an indication for a Season Pass 2. This is just my feeling, but I think some level of development has already started on the DLC characters if only at a foundational level. That said, I don't think we can really ever tell if any of this helps or hurts Geno at this point, though. Digging into the minutia hasn't really turned up much so far. We still don't know why Sakurai bought that Vifam toy dang it.