The main themes of echos were LGBT relationships and control. The main themes for Revenant so far seems to be single parent house holds/daddy issues and racism/xenophobia (it's shown in the intro cutscene and mention a few times by Mithrax) Given that these are largely left leaning talking points we can assume that Heresy will likely have abortion and immigration as the main themes. So there is a good chance Savathun will ask us to abort Xivus worm like we did hers, then using the Ahemkara she possesses, restore fundament for the lucent hive to return to. Meanwhile the guardian will be exploring the dreadnought trying to find a way to deport the lucent hive back to their home world.