He was awfully obsessed with his physical appearance for an INFP.
If there's one type that dislikes the shallowness associated with looking at physical appearance over personality/what's on the inside, it's INFP.
Of course, who knows what happens when you have such inhumanly high levels of fame? Lots of things could get messed up.
I think we can all agree on IxFP...but most of his songs are about concrete things and events, moreso than puttering around with idealism/searching for perfection. He wrote a few songs like that, but it's not really what he was about.
Not to mention, INFPs are not nearly as natural in the spotlight as ISFPs. Michael was the epitome of cool in his heyday, and that's also very common for ISxPs--being in touch with what's hip, cool, and going on right now.
I could see some reasoning for INFP--"We Are the World" and so on, pretty idealistic. But I still think there's a little more evidence in favor of ISFP at this point, so I'll stick with that.