It would be hard to top or even hang with Vangelis' score. This sequel will need to uniquely stand on its own, somehow.
The director has directed some pretty grisly movies, and some with weird, metaphoric and ironic twists & turns. His latest movie Arrival is worth watching, and gives some promise to how he may approach this. Arrival is a very slow, ambient movie that kind of tricks the audience with the ending (well it may not have tricked people to the extent I was fooled- I may have overthought it and expected a more complicated interpretation)
At any rate Arrival was one of the best sci-fi movies this year, easily.