So, like, is Earth itself being turned specifically into a Vessel for Adam?
The term is specifically "Adams' Vessel". While nobody knows what it means, I don't think the most straightforward deduction should be overlooked -- more here
. (In addition to what's mentioned there, the only other time I've seen utsuwa
(vessel) used in the context of NTE was the entry plug being called "the vessel of a soul" in Explanation of 1.01.)
The more likely explanation, to me, is that the Earth's surface is meant to function as a collective core for the life that formerly lived there. Thus we might already have a mechanism for what the L Barrier (or L Containment Field) actually is: it's a gigantic ATF being generated by all of these souls. An ATF of sufficient strength would be antithetical to the existence of other beings; sort of like EoE's AATF, all other egos would simply crumble before its power. If (and I do mean "if") any of this is right, then it might help explain other features like "barrier density" and core-ification categories; it could be a simple matter of how populous a particular area had been.
Though all that said, it's hard to get a good feel for what the exact end game here is. There's some possibility that it's all part of a long-term plan to "purify" Earth of the "original sin" (more here
). However, while the start of Shin gives us some further insight into what Gendo and Fuyutsuki's goals might be, it doesn't necessarily explain all of the weird post-Third Impact effects we've seen -- which, like the insanity in EoE, could be a result of multiple plans attempting to gain a foothold at once. For instance, how do you reconcile the formation of giant body parts with the creation of the Failures of Infinity? One suggests the core-converted surface is being used to create some sort of colossal humanoid abomination; the other suggests the surface has been turned into a "nursery" for evolving humans into Eva-like collective beings. So which one is it? Who is responsible for what? This isn't even taking the transformation of the Moon -- the real
elephant in the room -- into consideration...