I do wonder if someone reasonable actually sat down with him to explain Bitcoin (not someone like Saylor), whether he'd at least admit that there is a case to be made.

I think you'd have to acknowledge that bitcoin is "speculative" in the sense that it's not a productive asset, which is what Buffet is used to investing in. But then you'd have to explain that the speculation is quite reasonable given the arc of monetary history, and you'd have to get him to acknowledge the risks and injustices built up in the fiat system.