I wouldn't worry about a sequel (I'm still hoping for a prequel). Remember Hellboy II:The Golden Army. That just came out of nowhere.
I wouldn't worry about ever seeing anything from this movie again. It's on track two be one of the top 4 flops of the summer making only $39 million in it's opening weekend.
Like Hellboy, Pacific Rim is going to be a fan favorite.
Honestly what kind of world do we live in when below average stuff like Man of Steel and Star Trek into Darkness makes a ton of money and good movies like Pacific Rim gets ignored.