Even if we ignore what you call "pixel perfection" (which is actually more significant than that, as without fixed layout it's impossible for example, to lay im

Even if we ignore what you call "pixel perfection" (which is actually more significant than that, as without fixed layout it's impossible for example, to lay images where intended, or with an expected proportion with the text), it's simply that some tools (any form of annotation essentially) doesn't make sense on a variable layout. Of course, EPUB makes sense for allowing reading on a variety of screen sizes/devices, but expecting PDF to disappear ignores important use cases.