We could approach them again. IIRC it was something about the interactive features of PDF (forms, animations, conditional content), and poppler being designed to display things only, not to interact.
It would be good to ask them about this. It sounds like lots of features are not going to be supported.
GNU PDF is designed to handle all these features. The reason we removed GNU PDF from the high priority projects list was that it seemed evince would do the job. If evince is not going to handle all those features, we should put GNU PDF back in the high priority projects list.