I agree with your points #1 and #2 in your original post Nick_
With point #1 - allowing us to enter pixel dimensions directly into an 'edit' field - we would need some extra logic to guard against us entering pixel dimensions (accidentally or otherwise) into those fields that exceeded the dimensions of the original picture. But I'm sure that extra safeguard shouldn't need anything more than simple arithmetic to be applied to our 'typed-in' dimensions. (I'm assuming also that we are not considering the possibility of expanding or stretching or 'up-ressing' our images by using this proposed improvement - as that would be an entirely different topic than 'cropping' of course
And on your point #2 - showing the actual trimmed or cropped image dimensions in the EXIF area (or anywhere else) - Oh! yes please
... I've lost count of the times when I've wanted to know the size of my cropped image!!!