Something that's something of an issue for me at the moment with my kineticist's inability to do non-lethal damage. Merciful spell would be an ideal thing... except you can't apply metamagics to blasts. And for good reason, I have to say. But it can be annoying.
But then we have metakinesis, which is essentially a metamagic that you get in exchange for burn. So, maybe this could be extrapolated to allow Kineticists to take and use other metamagic feats in exchange for burn?
As a starting suggestion, how about this:
+0 level metamagics (although merciful is currently the only one) can be taken from level 1 and used for no burn.
+1 level metamagics can be taken from level 1 and used for 1 burn.
+2 level metamagics can be taken from level 5 and used for 1 burn (As empower).
+3 level metamagics can be taken from level 9 and used for 2 burn (as maximise).
All of these function as metakinesis and as such can be chosen to be reduced by metakinetic mastery. You still need to take the feat to be able to use these varieties of metakinesis.
Hopefully this should interact with Kineticist suitably without messing anything up. The +1 level metamagics are the bit I'm most uncertain of, so I erred on the side of caution and made it worse than it perhaps should be.
I'd love to know what people make of these.