This has significant consequences for companies hosting their private repos with GitHub. It's a huge security threat if the attacked has access to the source code. At the very least, GitHub should let people know if their repo was part of the hack or not. It's the most responsible thing to do.
Well, the hacker group claims to have access to the Github source code according to the linked article. And apparently, one lucky buyer with at least $50,000 can also have access.