Brutal Legend 2 could be a thing if Psychonauts 2 is a success.
At the very bottom of the page, there's a couple of questions and answers from developer Double Fine. One of which, name drops Brutal Legend 2.
"We've always said that we wanted to make sequels to both Psychonauts and Brutal Legend," wrote the developers. "We can't make any promises but if Psychonauts is a success for us, then perhaps Brutal Legend 2 will be more possible?"
Now you know how to make a Brutal Legend sequel happen.