I think a really cool (and geologically accurate) feature would be if the Create Water node took rock hardness into account when directing river flows. It could inform larger scale meanders/diversions in a river stream, which could also help accentuate some features (perhaps simulating an area where water is forced around some protruding bedrock as it cuts into the landscape).
Lately, I’ve been playing around with using hardness masks generated by perlin noise separate from the existing terrain to create more interesting erosion patterns (which also tends to help with creating foothills and other, more random, hills in valleys), and I think the create water device could greatly benefit from something like this.