He's definitely a good candidate. He's got the authority to pull this off too, but I will always stick to the mafia theory because it would make the most sense in the end.
And their leader being one of the Gorosei gives them the ability to basically do whatever. He obviously couldn't have been the only head judging by the fact Brook even knew who they were implying they were a thing pre Roger's
era. It's intriguing regardless of the outcome.