A crossover with VF just feels more natural story-wise. Judgment 6 and MIST, kidnapped ninjas turned to experimental killing machines, dying old men finding successors to their fighting style, the list goes on and on. If Team Ninja and Sega AM2 haven't caught on to this and acted upon it by now, I'd be surprised.
Hate to say it, but I really doubt VF will be getting a sequel any time soon. The series is way too dormant. DOA has a pretty decent chance on the other hand. I wouldn't want a full-fledged crossover but wouldn't mind if Jacky, Akira & Pai make a return.