I like the idea of managing the Burn in some way or another. One potential way is a burn pool, which could scale with level to help soak up excess burn to keep you from straight dying. A d10 hit die wouldn't hurt either.
Possibly just consider turning the burn requirement down on some of them. Maybe you could get one, 1-point infusion per [insert reasonable time period here; I was thinking per round] for free (which would increase to a more powerful one at higher levels) and then any additional would start to hurt.
Or you could have the burn slowly heal. I know that right now you can't heal burn at all, except for resting, but maybe if there were an extremely limited way to restore that over time. Maybe you could only heal burn equal to 1/4 your level per day, and only out of combat or whatever. Not a LOT, but some. Or maybe you could have a Wild talent that did that, or a feat, or even a spell. I can see that being a Water thing, TBH. Healing and persistence always seemed like a water thing.
Side note, not related to burn, but to overall survivability: Medium Armor proficiency would be nice, too -- maybe you could make it a thing that Earth kineticists gain Heavy armor proficiency, and Wind are restricted to only light, but to compensate can add to their AC through a dodge or enhancement bonus? Either a static one, like the Monk's WIS, or the Kensai Magus archetype, that can spend MP to do so temporarily? Or both?
Also, as a parting note, I completely disagree with anything Shiroi said or will ever say, forever.
