A lot of users asked this because it was commonly believed that an increase in traffic alone could get it out of idle. But the only kind of traffic that HP cares about is Google traffic, and if you hub is idle, it can't get Google traffic because of the no-index tag. So at this point, editing the hub is the only thing that can get it back to featured. Don't worry though, even a small edit like adding or deleting a character will do the trick. Or you can add extra modules like images, quizzes, etc.