The metafusionist is a kineticist who is also a student of the arcane arts. Rather than using constant practice to alter the way their powers manifest, they delve into ancient tomes of mystical knowledge, learning to bend their powers in the same way wizards bend their magic spells.
Study of the Elements (Su)
By researching the elements extensively, the metafusionist has learned how to push their abilities beyond what their bodies could normally handle. A metafusionist can use his Intelligence modifier instead of his Constitution modifier to determine the DCs of Constitution-based wild talents, the duration of wild talents with a Constitution-based duration, and his bonus on concentration checks for wild talents, and uses it in place of his Constitution modifier to determine kinetic blast damage.
He adds Knowledge (Arcane) and Spellcraft to his list of kineticist class skills.
This ability alters the kineticist's class skills and the key ability scores of wild talents.
Frail Body, Brilliant Mind (Ex)
The metafusionist's constant study has lead to him neglecting his body's condition and leaves him little time to train in other abilities, but he knows how to more efficiently channel the energies in his body. His hit die is reduced to a d6, and he receives 2+Int skill points per level. He can accept a total amount of burn per day equal to 3 plus his Intelligence modifier, and this limit increases by one at 6th level and for every five kineticist levels thereafter.
This ability alters the kineticist's hit dice, skill ranks per level, and the burn kineticist class feature.
Metafusion (Su)
The metafusionist can bend an shape the elements in ways that many kineticists can only wish they could. At 1st level, the metafusionist picks a metamagic feat for which he qualifies as a bonus feat, using half his kineticist level as his effective caster level for the purpose of qualifying for such feats. He gains an additional bonus metamagic feat at 5th level and every four kineticist levels thereafter.
When using a kinetic blast the metafusionist may apply one metamagic feat to it that he knows, treating his blast as an evocation spell with the same descriptors as the blast. To do so requires him to accept an amount of burn equal to the increase in spell level the metamagic would have applied to a spell (for example, applying toppling spell to a force blast would require him to accept 1 additional burn). Burn accepted this way cannot be reduced by infusion specialization, but can be reduced by using gather power or internal buffer.
The metafusionist cannot learn echoing spell, empower spell, reach spell, maximize spell, or quicken spell. If a metamagic feat requires the above, the requirement is replaced by the twice metakinesis, empower metakinesis, extended range infusion wild talent, maximize metakinesis, and quicken metakinesis, respectively.
This replaces the infusion wild talents learned at 1st, 5th, 9th, 13th, and 17th levels.
Metafusion Master (Su)
The metafusionist has vast knowledge of metamagic that he can use to more easily apply metakinesis. At 19th level he reduces the cost of all types of metakinesis by 1 burn (to a minimum of 0).
This ability replaces the metakinetic master kineticist class feature.
True Metafusion Master (Su)
At 20th level, a metafusionist has become so adjusted to the use of metamagic that his kinetic blasts he innately melds it into them. He chooses one metamagic feat he know that would increase a spell's level by no more than 1. That metamagic always is applied to his kinetic blasts for no additional burn, and does not count toward the normal limit of one metamagic per kinetic blast.
This ability replaces the omnikinesis kineticist class feature.
Way too much... Consider making a hybrid class instead? Probably with spells in place of utility wild talents with 6th level spell progression...
I've been thinking on this, and there seems to be a few inherent problems with the archetype.
For one, fewer hit-dice, higher Intelligence (and thus lower constitution) yet still using Burn...
Example, 3rd level character with an 18 Int, 14 Con (the most likely point spread)...
He'll have 6 + 4 + 4 from Hitdice, +2, +2, +2 from Con Bonus, and maybe +3 from favored class for 23HP.
His max burn is 7 (21HP of 23HP) and you let the max burn increase repeatedly which will never be needed... you'd probably be better off just saying there is no limit to the amount of burn you can accept. As is, that not only makes a 14 Con the absolute minimum he can do, but 18 the absolute highest Int he'll want to start with. :P
I guess the real question is, what's the purpose of the archetype? I don't mean that in a demeaning manner, I mean it as a literal question. Is your goal simply to have more meta techniques and a non-Con based burn system?
I think you'd be better off, if I may, just adding available techniques, tailor-edited for the kinetic blast. Ie: At 5th level you can choose to have X, Y or Empower Meta Technique by accepting 1 point of burn, but may only use 1 of these meta techniques at a time. Don't make it attached to an archetype, just as an option (sort of the way Advanced Player's Guide just added more rage powers for barbarians)
For the non-Con, I'd have to understand why you'd want that. My experience with the Sylph Archetypes (a -2 Con race, +2 Int race) was that Con was always as good as Int regardless of the system I conjured up, simply because of Elemental Overflow. The only way to really make it work is to replace Burn with some sort of mental-fatique (fatigued for a number of rounds double the burn cost? like Rage?) Otherwise, it's just not sensible to switch to an Int based system. :/
You're pretty much exactly right as to the goal for this: I wanted to apply metamagic to blasts first, and make it Int based second. I'd prefer it not to have access to spells beyond what one might gain from sources available to anyone (i.e. multiclassing, feats, and traits).
I was originally thinking of either having the nonlethal damage reduced to half one's level per point of burn or applying Int damage instead. The former may still allow the user to still take a little HP damage or additional NL damage before passing out, while the latter would make their blasts and talents progressively weaker as they use more throughout the day.
After some calculation I see your point regarding the burn damage though. At 20th level, using your example (someone with 14 Con and 18 Int at 3rd level), assuming the player puts all their ability score bonuses into Int, at 20th they'll end up capable of 12 burn per day (which is 240 NL damage normally) and an average of 112 HP. Even if I halve the NL damage, they can't take more than 11 burn without knocking themselves out, assuming they take literally no damage otherwise. Add the toughness feat into the equation and that's still about 132 HP, which leaves you able to take a whopping 12 damage with full burn. This could be partially mitigated by pumping 7 burn into your defense talent(s); if you put the elemental overflow bonus into +6 Con, +4 Dex, +2 Str, that adds 60 to your max HP if my understanding of Con bonuses is right (+3 to your Con mod from the size bonus, multiplied by 20 for your level), this leaves you 5 burn to use on other things throughout the day, along with having full or near-full bonuses from your defense talent (which would be absolutely fantastic for some combination of Flesh of Stone, Flesh of Wood, Force Ward, and/or Shroud of Water. You'll have 172-192 HP, so taking 70 from that initial burn (assuming we halve the burn damage for this archetype) leaves you 102-122 effective HP at the start of the day, or 52-72 if you take all your burn for the day and don't take any other damage. Still not a lot, but it's better than if you'd knocked yourself out.
Of course the problem with the latter proposed solution is that it's gonna reduce the Int mod, and in turn reduce the max burn (and as a result, reduce the max effective burn you can take to less than your max burn technically is). If I do the latter, however, not only would it encourage increasing one's Int as much as possible (both to mitigate the Int damage from burn and to keep blasts strong even later on) but would make Con practically a dump stat (at least as much as it is for any other class).
I was also thinking I may not use the d6 hit die. As you pointed out, with the NL damage from burn, he's barely gonna be left with any HP at all. This may not be necessary if I do one of the changes I mentioned; basically it's either apply the d6 AND reduce burn damage, apply the d6 AND change burn damage from nonlethal to non-scaling Int damage, or just apply non of it at all.
I'm not entirely sure about just strictly making choices for alternates to the available metakinesis, although it is a thought. Aside from the metamagic that metakinesis alreasy emulates, there's a lot of metamagic that could be interesting to apply, For example, if a kineticist has a level dip into a class that learns the ear-piercing scream spell, they could apply the booming spell metamagic to their kinetic blasts, allowing them to use sonic-elemental blasts. Applying thundering or sickening spell to an earth blast could deafen/sicken targets for an incredibly long time when adding enduring earth to the equation. One could apply sympathetic spell to a greater toxic wood blast to poison some important government official during a banquet miles away in an attempt to frame one of his colleagues or underlings for attempted murder. And keep in mind you're giving up infusions for this purpose, too. I feel like if you switch the base class mechanics to allow a choice of 1-cost metakinesis rather than sticking one with empower (and doing similar for the other metakinesis options) would make the main selling point of this archetype kinda moot.
Another thing I was thinking: should these metamagic effects extend the cast time for kinetic blasts affected by them as metamagic normally does to spells? This could prove a problem for using more expensive abilities in combat, since it means you won't be able to use a move-action gather power for it and fire it in the same round.