^ Chances are that was probably hearsay and not a reliable source. Unless Nexon says it themselves, you can't trust what other people say that Nexon supposedly said. (And sometimes you can't trust what Nexon says either but that's another matter)
Besides, the game thrives on new content, and new content includes the occasional new class. So long as Maple continues to grow, I have no doubts that there will be more classes in the future.
I think what you read was probably that Luminous was the last HERO that was going to be released, which is true.