Interesting write-up.

A few points of clarification.

Quote Originally Posted by MrThinker View Post
At the same time, those with the Echo who travel between worlds are “changing their aetheric frequency” to match that of another world so that they can interact with it.
Traveling between Shards, even for someone with the Echo, is much more complicated then this. In all cases we've seen of this happening (Ascians, Warriors of Darkness) the first thing that has to happen is for someone with the Echo to die, but not go to the Aetherial Sea (like they normally would). Instead, they go to Somewhere In-between the Material Ream and the Aetherial Sea which seems to match up to being in-between the Shards. Once they get to the Shard or the Source, they need to find and posses another body (usually already dead, sometimes still living) in order to interact with that Shard. Otherwise, they would just finish dying and be pulled into that Shard's Aetherial Sea.

So inter-Shard travel seems to be something that shouldn't be possible. And is only possible to do by somehow messing with the normal cycle of life and death. It seems to be something tied to the Ascian's desire to combine everything into one thing while Hydaelyn upholds the barriers that let individuals remain indiviuals, only in this case, it's on a dimensional scale.

Light and Dark
Light and dark are (apparently) opposing forms of energy distinct from elemental energy. We do not really know much about them, aside that too much of either is bad, with a flood of darkness leading a star to crumble into ruin and deforming what inhabitants are left (as what happened with the 13th), and a flood of light causing a world to fade away into blank perfection (which the 1st was in the midst of before Deus Ex Minfillia went over to absorb the excess Light).
This is true for the Shards (and probably the Source). What we don't know is how Light and Dark balance on the cosmic scale (scale of Hydaelyn and Zodiark), or if they are even in a state of balance at the moment. Unfortunately, this seems to be the scale the Ascians are really working on and we've really only got their word on how that balance is working out. And Hydaelyn's word. We know very, very little of how what goes on on the Shards and Source effects the larger balance of Light and Dark.