Almost everyone got it wrong.  There were a few in recent days who stuck out their neck and thought that the individual mandate would be upheld 5-4, but they thought it would be on Commerce Clause grounds.

Kudos to Ben Beutler at TPM, who noticed back in March, right after the oral argument, that Roberts was leaning toward uphold the mandate on tax power ground.  Read what Beutler wrote on March 26 of this year:

In a little-noticed exchange Monday, conservative Supreme Court Chief Justice John Roberts may have tipped his hand that he’s entertaining the possibility that the health care law’s individual mandate can be upheld on a constitutional basis that’s different from the one supporters and opponents have made central to their arguments.

For over a year now, observers and experts have assumed that the court’s final decision will hinge on the extent of Congress’ power to regulate interstate commerce. But the justices could also upend that conventional wisdom, and in a worrying sign for the plaintiffs on Monday, Roberts unexpectedly highlighted one way they could do that.

In an exchange with a plaintiffs attorney, Roberts suggested he’s skeptical that the mandate and its penalties can be treated separately and may have opened the door to finding that Congress’ power to impose the mandate springs from its broad taxing power.

And that's what happened.  Joey Fishkin got pretty near to it, too.