I'm finding it hard to figure out what this means from an execution standpoint. If the wrist goes lower, for example, it becomes harder to articulate the notes.
More of a lateral rotation as this piece is dealing with wide spaced chords. The direction of movement could be described by placing your hand flat on a table, and rotating your wrist as if you were motioning to wipe the table surface. The technical terms would be Ulnar Deviation and Radial Deviation. However, in the pianistic sense it is not pure Ulnar Deviation and Radial Deviation, but includes wrist rotation on all three axes.
Also, what do you mean by flexibility of the palm?
The part of the hand between the wrist and knuckles needs to remain flexible, elastic and supple. If the palm becomes too rigid it can restrict the fingers ability to articulate, cause unnecessary tension in the playing mechanism, and also create a disconnect between the transfer of energy from torso to the fingertips. A rigid palm also tends to place undue focus on playing with just the fingers, as opposed to involving the whole arm.
Have a look at pictures of hand anatomy, notice how the fingers extend into the palm. We don't normally think of this because when we look at our palm we see a lot of fleshy bits. A flexible palm sets our fingers up for maximal freedom of movement and ease of articulation.
I also noticed during the ascending passages that your entire forearm, wrist and hand tends to shift upwards when you move toward the 5th finger then drop back down when you play with your thumb. Try to use more wrist rotation to get your fingers in position as you move towards the 5th finger, rather than raising and dropping your entire arm.
With regard to LH, here is a good opportunity to practice LH discipline. A lot of long sustained notes. Think slow practice tempo, with quick, snappy, and precise LH movements between notes. The focus being what you do between notes. Slowly moving between notes here may not seem like much of a concern, but can magnify into problems when bringing the piece up to tempo. Don't drop your LH off the keyboard, it is not a good habit and can become ingrained if you are not careful. The LH should always be preparing for the next note. Again remember quick, snappy and precise. The movement to the next note needs to be deliberate and focused.