Thanks for the interesting question. Non-dual consciousness is the fundamental Truth behind all appearances of seeming separateness. Many have had it since the time of the Vedas or even earlier. This non-dual, Advaita can be experienced and realised on any plane. It can be felt behind the material universe, it can be experienced behind the varied play of life. It can be realised by quietening the mind and silencing it. This is what is generally known as the Advaita Mukti or the Buddhist Nirvana. The Gita takes us one step further wherein one can be inwardly free, Jivanmukta even though dealing with the manifold creation, the manifestation. This too has been achieved by quite a few including Sri Aurobindo (during the revolutionary days). To sum up the Vedantic realisations free the Purusha (the soul) from the clutch of prakriti. But it does not change nature which continues in its threefold mode. The self is released above nature, trigunatita, but nature is still inferior and ignorant, apara prakriti and not daivi or para prakriti. She is reserved still only for the greatest Gods and the Divine of course as Ishwara Shakti. But for humans the operating system is Avidyamayi Maya. The release of the soul comes by the liberating touch of the Vidyamayi Maya but there is obviously no transformation of nature. The only thing that happens is that the nature operating in the individual becomes quiet and full of peace reflecting the Peace of the Self. It also reflects the Light of the liberated Purusha in the mind making our thoughts luminous and at times open to a higher knowledge and intuition. As to the rest, most yogis are content to practice detachment and some degree of equanimity (the latter is not common though). All this keeps the lower nature calmer and not tranquilised but the beast is still the beast and it can raise its head from the subconscient in an unsuspecting moment as we see in the stories of some of the greatest of Rishis and Saints.
But transformation is neither saintliness nor a moral rectitude of life. Nor is it achieving certain abnormal or even supernormal siddhis and powers that Tantra gives. These gains still keep us tied to the lower nature even though it enlarged the fence and provides more variety of powers to fend and feed. That is why even the tantrics ultimately invoked the Divine Mother as Shakti to release the Purusha from her luminous and brilliant Maya.
Why this release did not lead to transformation is because the secret link between this trigunatmak prakriti and the higher Para prakriti was not found. Hence a gulf existed. The focus was on the mukti of the Purusha but the field of nature was modified through sattwasanshuddhi only to the extent that it would not obstruct the release. The link between the higher and lower nature however does exist but it cannot be found even in the highest ranges of the Mind nor in the immobile Akshara Brahman or the Sachchidanand Brahman that is everywhere and behind everything. Leaping from the mind to the oneness of Sachchidanand misses that golden link. For that one has to go beyond the Mind into the Supermind. We can say that the God realisation can take place at any level since He is everywhere but it is always through some veil, even though at times the most brilliant dazzling last veil that one may well mistake for the Ultimate Mystery. The Supramental realisation, on the other hand is to meet the Creator unveiled in His own house. It is there that the secret of transforming the lower nature is found by the action of the original Divine Shakti, transforming Sattwa into the plenary Divine knowledge, rajas into infallible Divine Consciousness and Force, tamas into the Divine Peace and the senses into conduits of the Divine Ananda.
