Pretty formidable theory.
I don't have much to add, but i would like to present my own humble piece of fanwanking. 1., The four beings seen during Second Impact form a single being. Seele seeks to recreate that being with it's "True Evangelion" project. The True Evangelion isn't any one Unit, but rather a merger of four awakened Units.
I'm basing this idea mostly around these lines:
Pretty straightforward, actually. Seele wants the True Evangelion, as a cornerstone of some ritualistic processes. Kaji's blurb implies (rather vaguely, i admit) that triggering a number of Units (four, if my guess is correct) is the way Seele wanted to do it, and Gendo getting Unit-01 to awaken via Shinji and Rei ahead of schedule was taking a serious spit into Seele's coffee. Hmm, actually i wanted to write more about this, but i think i already made my main point.
As for the four beings of light really being parts of one being, well, Lilith is still identified as the Second Angel, so it's a safe assumption that there is a single, definite First, too.2., Rei, along with the three other chibi-Reis seen in the trailer for 3.0 carry fragments of the soul of Lilith within them. Lilith's body still houses the majority of her soul, that's why it has to be restrained and seems to be "alive". Their role is to help trigger various Units and probably to serve as medimus in some sort of merger between Lilith, the Lilin and the True Evangelion.
When Gendo asks for additional resources to hasten repairs on Unit-00, Seele responds thusly:
I'm leaning towards the assumption that this means that they do not intend to have Rei (or any Reis) pilot an Eva anytime soon. Her role lies somewhere else. Of course, it is a possibility that they will give Rei a new Eva (07, 08 or something) in the future, and i honestly don't have a counter to that supposition.
However, we already have a precedent for a Rei being used to trigger an Eva:
Gendo knew that merging with Rei is, though under some pretty extreme circumstances, enough to trigger a Unit. I would suppose that Seele also knows this, seeing as how they seem to have a more clearly defined role for Lilith in their plans within this incarnation of the story.
From here, it lines up pretty well, i think. Four pilots piloting four Evas* that are trigerred by four Reis. The True Evangelion is born, Lilith gets reurrected by some means, Human Instrumentality Project gets underway, and... well, this is possibly the most speculative part of my already somewhat far-fetched post, but i think that Seele's ultimate plan is something along the line of:
a, Return humanity to the womb of Lilith
b, Have Lilith merge with the being that is formed by the merger of four different beings
c, Humanity gains the power to become one superorganism
d, Something something mankind reaches Nirvana
Not very evidential, i admit, but to me at least, it kinda makes sense.
*possible combinations: 01-02-06-08, 01-06-07-08, 02-06-07-08, depending on Unit-07 making it into the movie and whether or not Unit-08 is actually Unit-01
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