I personally like the status quo that PNGs don't encode orientation. I can dump PNGs when I'm debugging and I know I'm looking at the bits the same way up as the code is!
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"It is recommended that unless a decoder has independent knowledge of the validity of the Exif data, the data should be considered to be of historical value only."
Instead of either saying: "yes you must rotate it" or "no you shall not rotate it" to make everyone do the same thing. And if it were yes, they should also have made this a mandatory chunk since now they made it optional to read.