I have listed some of the possibilities and would like to know what you would like to see in the next release!
Support for OpenType tables that allow complex text layout, e.g. ligatures, smart glyph positioning, ...
Support for OpenType CFF fonts, i.e. .otf (currently only .ttf are supported)
Smarter text extraction
Optimization of images by using (external) image compressors
Support for Optional Content Groups (OCGs), i.e. layers
Support for tables when layouting
Page-wise box layouting, e.g. arranging boxes on a page given constraints like width, height and stretchability
Support for document outlines, i.e. bookmarks
Support for AcroForm forms
More complete support for annotations