I think your theories for restoring balance in both celestial matters, and matters of everyday affairs are most well put.
I myself must lean on the side of #3. We don't KNOW that we can harness the dark left behind by the killing of the shades. Furthermore I think the secret of contacting Angiens may be best served through them. It is certain shades know more of Angiens than we, and if our Alliances can cooperate, it may serve both our purposes.
A theory I myself have been pondering is this. Angiens, at least pictorially draw out the world of Marind Bell. While shades may be the darkness we miss, I wonder that the lightness of the Angiens is not that of the heavens themselves? If Shades represent the night, surely Angiens are the holders of moonbeams and starlight.