Well, although the document on the future/planned/fake changes on the Bending Arts seemed really interesting, and it summed up what I would like to see in the plugin, more specifically (and it couldn't not be this way) waterbending. But aside from the document...
I believe waterbending needs a way to chain abilities. Right now, it seems to me it is too "this slot does this, that one does that!" and it really lacks on the waterbending philosophy. As suggested by many, things like being able to turn someone's Torrent against the enemies, turn my OctopusForm into a WaterWave or blasting WaterManipulation from my Torrent ring, are missing.
The other aspect I feel like it should be implemented, not only to waterbending but also to earthbending, is the ability to move freely our element around. Sure, we can make tidal waves, rush water into someone or wash them to where we want, but the ability to manipulate water at out own will does not exist. Being a waterbender and needing a bucket to move water from a hole to another sucks.