The relatitivity of mind I like where you are going with John. And I believe there are a few ways to think about it.
If John views a screen that shows him what he is thinking, then the idea is that he is thinking about the screen and what the screen is showing him, which is what he is thinking. So there is an infinite chain, much like 2 mirrors opposite each other.
However, much like the mirrors, all that the screen would show would be exactly what John is already thinking. The duplication would in fact be hidden, as all John could see would be the immediate screen - he would necessarily be unaware of the infinite chain behind what he is currently seeing. You could argue there are hidden multiverses beneath the first image, and I'm ok with that - but it doesn't really prove much to postulate I don't believe, at least here. John the 1st would only be aware of the immediate image. and as all the images would be the same: thinking about a screen that shows me what I'm thinking, and all the johns would be thinking the same thing... it is exactly like looking into a mirror that can show you what you are thinking. which depending on your poker or people-reading skills... well never mind that.
And even if John could think infinitely - which is maybe what you are saying, all those thoughts would be identical. Infinity that has a singular scope is really just singularity when considering the singular scope.
So I'm not sure how that proves anything - even in the thought experiment it exists in - about the objectivity or subjectivity of mind. Certainly an interesting start, but not sure how to get from the thought experiment to objectivity and subjectivity. Perhaps you could elucidate?