I've been thinking that if we can't have a Kairi tutorial/opening segment, I wouldn't mind playing as Namine for the introduction portion of the game. Something could stir her consciousness within Kairi's heart, and she could be trying to figure out what it is by using her power to connect with other hearts, which could be visually represented by "diving into" the hearts of the various protagonists-- the way I see it in my mind's eye, it would be like a sort of "hallway of hearts" maybe modeled after Castle Oblivion, where she goes through different doorways to reach the inner sanctums of the other characters and investigate the "disturbance in the Force" (so-to-speak).
The segment could end with her being confronted by some Very Big News (which we as the audience may or may not grasp right away) and deciding she needs to get the information out through Kairi, somehow.
I realize this won't happen for all sorts of reasons (Namine doesn't fight and blah) but it would offer the opening of the game something more than, "press this button and that button, tilt the joystick to run" etc.
I really don't want her to be a PoH. I'm tired of the purity narrative that surrounds women in KH. If there's going to be another OC PoH it should be Ven. He fits the role better than Namine.