If we discover laws of physics that only seem to be active in the brain, that would convince me. If we discover that the brain sometimes violates the laws of physics as we know them, that would convince me. If we build a complete classical simulation of the brain and it doesn't work, that would convince me. If we build a complete classical simulation of the brain and it works differently from organic brains, that would convince me. Ditto for quantum versions, even, I guess.

And there are loads of other things that would be strong evidence on this issue. Maybe we'll find the XML tags that encode greenness in objects. I don't expect any of these things to be true, because if I did then I would have updated already. But if any of these things did happen, of course I would change my mind. It probably wouldn't even take evidence that strong. Hell, any evidence stronger than intuition would be nice.