I always wondered how long it would be before the studios realized, “Why have a three hour film when you can have two 90 minute films instead?”
sigh.
I believe the first film is entitled “Kill.”
The second, “Bill.” 
And the prequel - “Must”?
Well I’m sure that won’t screw with the pacing at all.
That seems to be the Hollywood trend. The Matrix and Terminator3 are both “half movies”. Very annoying.
But there’s a difference between The Matrix, Terminator 3, and (my perception of) Kill Bill. The first two have been made into franchises, and very effective ones. The first Terminator was made to be a stand alone, but people liked it so much, it was made into consequent movies, plus comics, toys, etc. The Matrix was designed to be a trilogy. The first movie is a stand alone, but the sequels are supposed to finish up a bigger picture.
To my knowledge, Kill Bill is a stand alone story that really has no point being split up. It looks fun, and I know they do it for seemingly everything nowadays, but I don’t think there’s much push for a toyline, comic series, or franchise to come out of this film. A stand alone storyline should be just that…stand alone. Sure, there may be more to build on with the characters after the initial story is told, but that initial story should be told in it’s entirety first.