Well, in the words of Professor Hubert Farnsworth, "Good news, everyone!" The film opened today to a $9 million, which is a record high for any Warner Bros. picture and more than 20% better than any of the studio's massively successful Harry Potter films.
Legendary Pictures, who underwrote most of the film, are currently in the final stages of a breakup with Warner Bros., and since they own Pacific Rim, it's been widely assumed that any even remotely good news for the movie could nudge Legendary in the direction of a sequel, if only because it gives them a piece of potentially valuable intellectual property to mine for future films, video games, comic books and other product tie-ins. Most of the films they've developed over the years they've been in business with Warner Bros. belong solely to Warner for the purposes of IP discussions.
While the U.S. box office has not been kind to Pacific Rim--it has not, and is no longer expected to, clear $100 million domestically--the international market has led it to (slight) profitability so far, and there's still a few markets, including Japan and Brazil, where the film has not yet opened. This is increasingly common for big franchise movies as the international market grows and becomes more significant to studios; Men in Black 3, which made less money than either of the first two movies in the U.S., was huge internationally and has actually become the biggest moneymaker in the franchise's history. As a result, months after its disappointing opening weekend Sony announced they were fast-tracking a sequel.