They went with that for Xrd because they thought forcing fights might get in the way of the story, Dragon Ball story is basically fight after fight, no way they wont let us play through them.I wonder if that's the approach they will take with it though.
It works great for GG, since it doesn't have an anime or anything so it gives us a way to watch its world, but Dragon Ball already has that covered. If they go for their own new storyline it could still work, but who knows.