My teachers think that:
Rivers will come up for the physical geography content (as you said), and potentially something about desertification or weather and climate.
They don't think ecosystems will come up because that was 2015's main text. They also think that for the case studies, coasts and desertification are most likely as they haven't asked that yet throughout the new specification from 2014+. On the other hand, WJEC might not want to be predictable and give us something else...
For human...
They think there'll be something about access to housing and the services one for the case studies as those are the two that haven't come up since 2014 (new spec). For the main body...they say that national parks haven't come up in a while.
How are you revising? I'm finding difficulty trying to...