Hi, thanks for such an extensive and interesting text. At great risk of sounding like a new-age hippy, here's my own take on what wildness is.
It's not something "out there", it's in everything, including us. In a way, there is no zone 5, because it's all zone 5. It's either sick or healthy. We mostly make it sick. Permaculture can be used to learn how to keep it healthy while getting what we need to survive from it.
For sure, it can also be used to bolster arrogant people's mistaken ideas about the universe and our place in it. It seems to me that's the predominant use at the moment.
In a way, also, it's true that there's no "wilderness" left in Europe, except perhaps that bit in Poland, but that's hardly surprising because we made up the word to specifically exclude any human intervention. We set ourselves up to remain in a language trap of our own making.
I tend to use "wilderness" as synonymous with "a wild place". I guess I'm wrong, technically, but it's hard to write or think of the concepts rationally when the only word we have is a thought-trap. "The Wild" might be a better term. I think "wilderness is not much use in the lexicon of rewilders, because all we can do is leave a place alone, and if every inch of where we are has already been tampered with, it's "impure" already and thus, as some authors imply, there is no hope.
I think that realizing the true nature of wildness, and implementing that into our philosophies, can help remove the hurdles imposed by the ideas behind "wilderness". There is no way to separate us from the wilderness, except by dying out. Wildness exists wherever humans exist, and anything else (i.e. separate from) is only a figment of our civilized imaginations.
Thinking this way leads to intelligent manipulation, just like every other species manipulates its habitat to make it a more conducive environment. Our unintelligent manipulations make it sick, but just like a slave is still a human, domesticated wildlife is still wild. Wheat may be domesticated and sick, yet if we left it alone over some generations it would become strong and healthy again. I may be forced to do certain things against my will, but that doesn't mean I have no will. I am still wild. I am "self-willed".
Our language deeply affects our thinking, so we need to throw off the bad thinking caused by limitations imposed by language. Zone 5 is wild, not interfered with by us, and we do that in order to learn from it what our place is in it. We don't need a piece of pristine land never interfered with by humans, all we need to to stop interfering with a patch and observe what happens there. Then we can compare it to our observations of interfered with areas in order to see what we are doing wrong.
Perhaps it's necessary to live somewhere where there is no wilderness before you can see that wildness is everywhere. Words like wilderness obscure the truth because they were defined by people who saw themselves as separate from the rest of life. We don't need to work to bring back wildness, any more than we would need to work to bring humanity back to a slave. All we need to is to release our slaves from their bondage.
Gradually, one side of my garden has become almost completely wild, and the other is on the way. Each year I need to do less and less, yet still it has things I can eat. It's a learning process.
The universe is "one change". Don;t listen to people who believe you have to go back to some previous time (which is impossible). We made a big change, and wildness will adapt to that, just like any other. Even if Fukushima turns out to be an extinction level event, or some other human stupidity does, it's unlikely to make earth Mars-like. Something else will happen, like with the previous ELEs and wildness will continue, with or without us. It's arrogant to believe that humans could destroy wildness.