I think there is a clue when the Buddha was asked "Who are you?"
Buddha thought for awhile and then said I am awake.
Buddha did not say I am the son of a king, the father of a child and a husband, he did not say he was the head of a spiritual order.
I am Awake
A Brahman saw the Buddha resting under a tree in meditation. The
Brahman was impressed with the Buddha's disposition and demeanor. He
asked, "Are you a god?"
"No, Brahman, I'm not a god."
"Are you an angel?"
"No", replied the Buddha.
"You must be a spirit then?"
"No, I'm not a spirit," said the Buddha.
"Then what are you?"
"I am awake" he said. In modern terms it is not a long stretch to say I am consciousness. Well if I am consciousness or I am awake, is there any historical figure the Buddha would point out to us? Is it not probable that those who are trying to establish historical figures waking up have missed a fine point? It is not the historical figure that changes, it is their state of consciousness.
One who has thus gone would then be one who has gone out of the awareness of the world seen as things to a state of seeing all as an expression of consciousness.
We are all potential Buddha realized beings so we are all potentially "One who has thus gone." The spiritual preparation does have steps of purifying intentions and disciplining an unruly sense of self. But the emphasis is more on realizing awakeness than on categorizing our unpolished diamond nature.
So for me the question is what can I do to know in my heart without wavering or doubt that "I am awake." No more illusions then. Perhaps that is the going beyond, going beyond illusions. More than that is difficult to say with certainty.