The prevailing consensus among appellate lawyers that I know is that the ultimate opinion in this case will look like Judge Sutton's concurrence in the Sixth Circuit. Sutton was a law clerk for Justice Scalia, and they still have a close relationship. The fact that he voted to uphold the mandate does not guarantee a favorable outcome for the mandate in the Supreme Court, but the Justices may find his reasoning persuasive.
The opinion is available in full
here. I think it is worth reading if you care about the issue.
Sutton's opinion starts on page 27.