The Vince Vaughn returning and Kiera Knightley rumors were just that: Rumors. Nick Van Owen(Vaughn) was never considered for return(Although I agree, he was one of the best things in the second film, and one of the few characters worth revisting).
The Monahan draft featured cameos from a few characters, the largest of which being Hammond in a role about the same size as his in The Lost World. Grant was an extremely minor role.
It centered around a new character being involved in the cloning of new and improved dinosaurs based out of a castle in Europe. It was suggested that the lead character would be hired to lead a team of intelligent dinosaurs in a film that featured genetically altered dinosaurs as actual characters, possibly going so far as to have them outfitted with weapons or them being able to communicate with humans.
It was a sci-fi action adventure.
However, because the script was leaked and met with quite a bit of negativity, it's been under a slew of revisions. How much, if any, of Monahan's draft still remains is unknown.
I personally think it's a horrible idea, but at least it's original.
The end of The Lost World ruined an otherwise fine film- Think of how great it would have been if the movie ended 15 minutes sooner, fading to black and the credits when the Rex roars in front of the city skyline, and then bursts the the sign and heads into San Diego. It would have been one hell of a cliffhanging, and could have perhaps led to an intelligent sequel. But I digress.
The third film was a total joke, and is better left forgotten.
While part of me loves the idea of a cybernetic Rex with lazer eyes and a gattling gun mounted on it's back, I think it belongs in a Dinoriders film- not in Jurassic Park 4.
t: 
