It's hard to say a healing ability is crucial when literally only waterbending has them. Other benders don't need them. My main problem with Rejuvenation is that, in the series, water had direct contact to it's healer because it was used as a catalyst to regenerate, the idea being taken from reiki practices and the idea that all life consumes water. Using a plant to heal yourself feels very off in this sense since it can quickly regenerate itself with waterbending, but then we'd get into the debate of plant and animal cells. Mostly swamp-style bending was very rigid and stale compared to the northern and southern styles and in general very offense. Your cacoon idea feels like it could go somewhere, in my opinion, but it's hard to say. Mostly, I see a fairly pointless barrier or a plant version of octopusform. Razor leaf, with a name tweak, would be fairly acceptable in my opinion. Believe it or not, it's canon.
Also noteworthy, most of these ideas aren't "new". They have been suggested on here at one time or another.