To me the most important thing is this:
In general a world that feels "alive" and not just flying over (enhanced) static satellite images. So; AI planes, trains, (believable) road traffic, ships, animals, power lines, windmills, smog, smoke, etc.
The sky is already very much alive with the new weather and aerodynamics engine. Birds could add to the experience as could snow and other seasonal effects.
I really hope they will try to eliminate shadows from the satellite images (using some kind of algorithm and Azure), as they are static/baked and it will look strange at different time of day. Same for cars on roads. Hope they will find a way to make AI (road) traffic look realistic without using too many resources