More fleshed out companions, with really detailed questlines, backstories and character... That would be no1 stretchgoal for me. if you can do that, then add maybe two more additional ones. Keep the cast big enough but detailed, and deeply developed.
I am all for new stretchgoals! More companions, more world content and more quests. But whatever more money we drop for it, it should still make the game be release this year! Important!