In a recent interview with io9, Goldsman shared several of the ideas that he came up with for the film that thankfully never happened. None of the ideas seem like they could have really worked. When asked about the sequel, this is what he said,
Oh no no, [there was] never a movie. I mean, we wrote a prequel [and] a sequel. We had a really interesting prequel, which was the first outbreak of the virus, during a Thanksgiving Day parade, which was awesome. We did a really interesting prequel that [took place] later. Which was right after the first… really right when the population of of humans became pretty decimated. And it was this sort of trek to Washington. Which included a dark seeker elephant that had broken out of the zoo.
Then we did a sequel, that started with Neville again — and you realized that he was cloned. We’ve tried every which way. In fact if you’re available you could be in the next movie. It will never happen but we really enjoyed trying to make it happen.