Immediate thoughts:
1. Very interesting theme! As a fan of deckbuilders, Memory, Mentor, and Intensify, I find this to be a fascinating concept, if a necessarily fiddly one keeping track of what augments are attached to what powers. I love the idea of looking for clever synergies to hand out to my fellow players.
2. Do you shuffle the Augment deck during setup? This is not mentioned anywhere, so by default the answer is no, so you'll be encountering these cards in a fixed order each game which doesn't feel right.
3. As far as I can tell, element markers are only useful for purchasing augments at a 4:1 ratio and the actual elements involved don't matter. Yet the top effect of Hone Powers has restrictions on which elements the player receives? I feel like something's missing here.
4. What happens to the top effect of Hone Powers when no Augmented powers are in play? The implication seems to be that in that case you just ready one marker, but this means that the "Ready two element markers" will often be misleading. This could be rephrased for clarity.
5. All Augment cards appear to be listed as Fast; does this mean that they make their attached Power Fast? The "Augmenting Power Cards" special rule already specifies that Augments are played with the card that they are to attach to, so Augments themselves shouldn't have timing.
6. Augments stay attached to their Powers as their Powers move between Play, Discard, and Hand, right? The "Keep Augment cards behind..." reminder text seems to imply this, but it isn't explicitly stated.
7. The energy cost of Augment: Abundance is listed as "1" instead of "+1."
8. I assume Augment: Forethought counts both Power Cards and Augment Cards in your discard? This relies on the answer to #6.

I think the idea is very cool, but I unfortunately think the result is likely to be on the weak side outside of some specific broken combo for teammates. You're like Mentor being able to give out bonuses to teammates, and you're like Intensify getting to improve specific qualities of existing cards, looking for powerful synergies; both of these things I love. But unlike Mentor you lose access to element markers facilitating Thresholded Majors, which means you're probably doomed to playing un-thresholded Majors all game; you could try going bottom track but you're just going to be a cruddy minor-power spirit for the most part. And Intensify gets to improve the vast majority of powers they play; here you need to be really careful in deciding which cards to buff, and buffing an ally's card means not buffing your own. My gut is that you'd end up either buffing your allies to do cool stuff while you do very little, or you desperately try to draft both the right powers and the right augments to do something meaningful.

1) Glad to hear that you think the idea is interesting! The idea of looking for those clever synergies is exactly what this is going for, but I imagine the potential to break the game when they are permanent upgrades and shareable with your teammates is very high. Probably why Intensify is the way it is :)

2) Ah, that's an oversight on my part, the deck should be shuffled. I'll specify that in a later version.

3) You still have the Unique Power Element Teachings, so Element Markers can still be used for that, and need to be acquired in some way to keep it useful.

4) You are right that this could be reworded to be more clear - since there will quite often not be a augmented card in play, e.g. on early turns. Thanks.

5) The Spirit Island Builder that I am using to make everything does not have a "none" option for fast/slow, so everything is just fast. Improving the template for the Augment deck would have to be a part of development at some point, but not a huge priority this early.

6) The test for the special rule says that Augmenting is "permanently attaching 1 Augment Card from their hand to (a Power Card)", I think it is clear enough.

7) Noted to correct it later.

8) I intended it only to count Power Cards, but I can see how that is not at all clear. I'll correct this as well :)

I could imagine you're right! I've only playtested this a couple of times a while ago and it was in solo, which is definitely not where the aspect is most exciting.