You always hit the ground running, as they say.
My "we" was the very mundane collection of individuals who started talking about Sloterdijk and kicking around his ideas about 13 weeks ago, and the "decision" was put in quotes because it wasn't really one but that we had formed a very vague, non-binding consensus that spheres was more a metaphor than anything else.
It is my belief that we (and this is the more general, we human beings alive on this planet at this time) cannot exist without limitations, if that is the correct word to describe them. I tend to think of these as boundaries, but they are also restrictions and constraints and some of them we create and some of them are presented to us by others and some are products of the situations in which we find ourselves. I'm pretty sure right now that Mr. Sloterdijk and I agree on this point, but I'm not convinced, which I'm sure you'll find hard to believe, that our interpretation of their meaning. But, I could be all wet, too. I think sometimes that the very notion of "space" may be the complicating factor here.
For example, in what or which (the very question colors the different possibilities of answer) space are you and I now? Where is this discussion thread taking place (if we are to include @madrush and @patanswer who are contributing as well)? The bits and bytes that constitute its potential for physical manifestation may be on a server in Colorado with identical copies existing on other servers in Arizona and North Carolina, but that's certainly not the where of the discussion. And while you may join and contribute from New York and Marco from Colorado and TJ from somewhere else in the EDT-zone and I from Germany, none of those places are definitive of the space in which the discussion takes place. That is to say, any space that is conceived in regard to this discussion is simply irrelevant. The whole question of space just doesn't matter. This is what I understand, at least in part, by aspatiality, as our friend Jean called it.
This is not to say, of course, that when I or you or anyone else who reads what's being put out "here" and stops to think about it and reflect upon it or even think about formulating their own response to any of this that it doesn't happen in some space. That space is, however, an abstract one, though we might also link it to a physical one (like my study, for example in my case, even that's often only where the actual writing of those formulations take place) but that space has no constituitive relationship to the "discussion space". Again, it doesn't really matter, hence I feel no need to even think about it. And since it doesn't really matter to me, in spatial terms, where this discussion takes place, in contradistinction to what I think Mr. Sloterdijk is saying, it need not be spherical or have any shape at all. I don't know why it would need one, but I keep getting the impression from Mr. Sloterdijk that perhaps I should. But, perhaps that's why I have so much trouble understanding him because I don't always get the necessity of what he's trying to say (and for me it was that way with spheres from the beginning).
Now I would be the last to maintain that the Magical and Mythical are no longer with us. I don't consider myself a rational person for that very reason. They are very much alive even if they are not always actively in our awareness. But, I also think that Gebser was making clear, and you are reinforcing the understanding, that each of these structures has its own rules of engagement, if you will. Anyone who has actually practiced magic (or magick as it was often referred to in order to distinguish it from the sleight-of-hand on stage) knows that the very first thing act one performs (after proper ritualistic cleansing and preparation) is the drawing of the magic circle. This is perhaps one of the most intensive acts of boundary-setting that one can do. I mean, if you're going to be fiddling with the fundamental forces of the cosmos in order to achieve your one, singularly defined act, it's a pretty good idea not to be too generous about who/what is in and who/what is out.
It is very clear to me that in regards to magical associativity this is absolutely essential. This feeling leads to that connection and on to yet another notion and the essential and fundamental connectivity of all that is suddenly spreads one out over the whole cosmos itself. I don't know about you, but my little mind has trouble with all that. And so, we learn to focus, to separate and exclude what is necessary from what is not, what is relevant from what is not, and this ability to set boundaries, impose limitations, engender constraints -- whether we are focusing our wills, our vision or our thoughts (just to touch upon the last three active consciousness structures) -- is essential to our individual, hence our collective survival. If that's what Sloterdijk is telling us, I'm all for it, but I'm not sure. But what is equally clear to me is that there are consequences to setting any and all boundaries/limitations/constraints. This is not a bad thing, it's a good thing, and it's the Magician's lesson to us: if you take in everything, you have nothing; if you allow everything to affect you, in the end you can be nothing.
The very first lesson of the very first sephirah we encounter on the Kabbalistic Tree of Life is discernment. We start learning this lesson very early, at least when we take our first breath. (Yes, some, among them Mr. Sloterdijk, move this moment even further back, but I'm not convinced of that and the argumentation and evidence I've encountered and been presented with hasn't yet convinced me otherwise, so I'm going with my own model in the meantime.) But, too many people don't seem to get it. As a result there are a whole lot of folks in the world who are, as you so eloquently put it, "a hodge podge of movies, theories, medical interventions, diets, urban environments, air travel, competition, etc., all of the glories of the Modern mixed with a lot of war, injustice and rigid boundary making" (whereby I'd replace "rigid" in that last phrase with "arbitrary").
What you describe is a kind of hell, at least a hell on earth, and as Jordan Peterson points out, one thing that makes hell Hell is that it's a bottomless pit: there's always someone who finds a way to make things even worse than they already are. Well, obviously the first thing any of us has to do is to find a way not to make things worse. For me, the obvious second thing is to find others who are trying to make things worse as well. I would like to think that's precisely what we are doing "here", wherever that may be.