What remains unanswered is:

What happened to Elle.
How Beatrix and Bill met and their relationship before the church massacre.
The backstory of Bill.
Why he formed a group of assassins and the backstories of the rest of the deadly assassin team - especially Beatrix's (we only got Ishii's backstory)
What happened to Nikki and does she intend to avenge her mother's death.
What kind of life had Beatrix and B.B. formed for themselves once Beatrix Killed Bill.

These are all things that should be addressed in the film. If they all are.. it will make one hell of a movie!