In the strictest sense, we are all without knowledge, but this is not what I think the question is really asking.
In the face of our utter lack of true knowledge, I think most of us make unconscious assumptions on which we base everything we think of as knowledge. We assume that our senses are accurate and faithful to what the universe truly is. From that we develop individually varying criteria for what meets the threshold of knowledge (vice theory, rumor, superstition, fiction, etc.)
That individual criteria of knowledge is an outgrowth of our desire not to be adrift in a chaotic experience of the universe. It might be that there are people out there who are consistently conscious that they do not know anything, but I have never met anyone who has embraced that kind of true agnosticism.
More to the point, I have a hard time even conceiving of what that experience would be.
I guess my answer to the question is "I do not know."
If one asserts that it cannot be known whether or not something exists, they are saying that there is cannot be evidence for something. If there no evidence for something, then there is no reason to believe. So, someone claiming to be an agnostic is by default claiming to be an agnostic atheist.
"Pure equilibrium" is inappropriately applying numeric values to something which is not inherently numeric. Granted, you could assign number values to aspects of agnosticism but these would all be arbitrary. By one analysis a person could be 50/50, another 40/60.
If we take "pure" to mean they insist that knowing God's existence or non-existence is strictly impossible and will never be knowable then yes, it is absolutely possible to be that agnostic as opposed to leaving a little room for humanity to figure it out in the future.
If by "pure" you mean there's nothing in the person's subconscious that disagrees this is difficult to say. I don't know enough to say it's impossible but it is clear that a person who insists they have not a shred of doubt that they don't know God exists might be mistaken and really have some doubt about it somewhere within them.
I don't think it's possible to be perfectly neutral about any point of view. A person who says he is 50/50 would only have to be 49.999999999999 % or 50.0000000001% to be out of a state of perfect equilibrium. If your belief/doubt were that close, you might to be able to tell you were leaning one way or the other, but you would be. To truly have "pure agnosticism," your belief/doubt would have to be balanced on a razor's edge, which I don't think is possible.
I believe that pure agnosticism can't be possible because of the fact that everyone has their own sets of belief in which they are entitled to. Also, an individual might have a strong belief of either the existence or non-existence of God but then again through the words of others, that individual might change his/her own thoughts and use that as a basis.
Pure agnosticism does not exist. This is because it goes against what many people believe. Its also somewhat of a subjective topic and can be viewed in many different ways. What is good, bad or believable differs from person to person. Pure agnosticism might be ideal but it is not possible.
The definition of agnosticism is that the truth of certain claims (i.e. the existence or non existence of God) is fundamentally unknowable. So for someone to be a pure agnostic simply takes the belief that certain things are unknowable. It is therefore completely possible to be a pure agnostic, with very little effort.
No I do not think pure agnosticism is impossible. Agnosticism is when someone is not sure of the existence of a god or not. I consider myself to be completely agnostic. I really have no clue if there really is a god out there. I see both sides of the coin and just cannot decide. So I do not think it is impossible since I am an example.