I would like to see a better annotation tool set in the inbuilt pdf viewer. Also very handy would be a function to add entensive notes and a way to search the notes themselves. A full list of notes across all references in a single view mgith be a great way arranging thoughts while writing manuscripts.
Another feature I long is an inbuilt text editor to put together all notes from the refrences and start editing the manuscript. This way one can write notes as if they are writing the maniscript itself and then easily arrange the notes and make edits. Would not that save quite some effort?