Though while saying he was working on it Guillermo del Toro also made it clear that no studio or production house has actually signed off an anything. So this shouldn’t be taken as a sign that Pacific Rim 2 is actually happening, just that del Toro wants it to happen.
In his favor is the fact that while the movie did poorly here in the States with only around $102 million in box office, the international story is very different. It pulled in well over $300 million overseas taking its total to around $411 million. With an estimated budget of $190 million that puts the movie in respectable but not exceptional profit territory before considering DVD/Blu-ray sales.
It may be the a sequel would have to be made on a smaller budget, but there clearly is a market. In my review I wasn’t entirely complimentary of the movie. It has its moments and it’s fun aspects but I don’t really get the level of obsession that some fans seem to have. Nevertheless those fans exist.
Del Toro doesn’t give much in the way of script specifics, but it seems that it will not be a prequel and Raleigh Becket (Charlie Hunnam) and Mako Mori (Rinko Kikuchi) will return. So if I was inclined to bet I would be looking at an exploration through the rift. Which will, arbitrarily and completely ignoring any actual logic require giant mechs.