DQIX is a true sequel in the series, regardless of platform. If it breaks sales records, which is possible given the series and platform, expect more to follow. Maybe more direct sequels on future handheld hardware, and almost certainly more spin-offs on DS.
We all knew DQX was coming, but as far as I know it's not standard practice to formally announce sequels to titles you've yet to release. That's what raised my brow. And yeah, they can be arrogant, they can be whatever they want; it's DQ after all, but still...