The story isn't that they planned to do this, and it is unreasonable to conclude that the plan was ineffective.
The story is that they developed a plan to do this. I'd be shocked if China didn't have a plan (or a dozen plans) for the conquering of Taiwan. I'd be horrified if they actually planned to invade Taiwan. Military people need to practice between real action, and drawing up contingency plans is a way to do that. It's healthy, and prevents much stupidity from seeing the light of day.
For example, from thinking about this, they may be led to realize that net censorship is ineffective and counterproductive unless it is undertaken on a brazen scale. That would be good, and IMHO more likely than that it will lead to real attacks on Wikileaks.