I read the link and have been thinking about it for a while. I think it's somewhat pertinent to the recent discussion of free will. OP or others can correct me if they think I'm missing something.
It looks to me that Goran's article boils down to two basic ideas, one which I don't think is new and the other which seems novel to me.
First is the idea that there is no evidence for objective reality. Any evidence we might consider is automatically subjective because we must receive and consider it in our experience, thus what we consider is subjective consideration of a subjective experience rather than evidence of anything objective.
I think this is accepted by anyone who accepts the coherency of solipsism. I don't think madnak could assert that the assumption of objective reality is an unnecessary foundational assumption if he also thought there was evidence for the existence of objective reality.
However, Goran takes this one step further and I think it's in this second idea that he gives us pause. As I understand it, that idea is that not only are we disconnected from objective reality by our isolation within subjective experience, but our concepts are themselves a kind of experience and thus can never be anything other than subjective concepts built on subective experiences. So the very concept we call "objective reality" is a subjective concept, thus self contradictory. Subjectively conceiving the nonsubective is as incoherent as the concept of "something that doesn't exist". Or, make your own analogy.
So in Goran's view, not only is there no evidence for objective reality but our very concept "objective reality" is incoherent. It makes no sense to even talk about it.
I think it's an interesting idea.
I'm not sure, but he may have taken it even one step further to show that all our concepts are incoherent. Of course if he does claim that then he would have to look at the implication that his article itself is incoherent.