Bhikkhu Thanissaro was definitely wrong is explaining viññanam anidassanam is beyond the six sense media because SN 35.23 says there can be nothing experienceable beyond the six sense media.
Since Nibbana, in Ud 8.1, is described as a sense object (ayatana), how can Nibbana be an object of sense media but viññanam anidassanam is not an object of media?
Also, DN 11 says in viññanam anidassanam the four physical elements "have no footing" (rather than "cease without remainder") therefore viññanam anidassanam is not something completely disconnected from the four physical elements.
Also, viññanam anidassanam is certainly not a consciousness of arising of Dhammacakka, The Eye of Wisdom, because the Dhammacakka is described in many suttas (such as SN 56.11 & SN 35.74) relating to the Four Noble Truths and Three Characteristics.
In the two suttas where viññanam anidassanam is mentioned, namely, DN 11 and MN 49, no listener of the Buddha gains enlightenment. This shows viññanam anidassanam is not the arising of the Dhamma Eye nor related to Buddhism at all.
DN 11 and MN 49 are both suttas of Buddhist propaganda spoken against or mocking Brahmanism (and probably not spoken by the Buddha himself). The verse about 'viññanam anidassanam' is spoken to Brahmins & Brahma gods, who don't believe in the Buddha. The Buddha's reply is related to the Brahmnanistic doctrines, using Brahmanistic terminology. For example, MN 49 says:
Consciousness that is invisible, infinite, radiant all round—that’s what is not within the scope of experience based on earth, water,
fire, air, creatures, gods, the Creator, Brahmā [1st jhana], the gods
of streaming radiance [2nd jhana], the gods replete with glory [3rd
jhana], the gods of abundant fruit [4th jhana], the Overlord and the
Now, MN 49 says viññanam anidassanam is not within the scope of experience of 'The All' yet SN 35.23 says anything not included within 'The All' is beyond range of experience. This apparent contradiction is explained simply by distinguishing that 'The All' in MN 49 is the Brahmanistic meaning of 'The All' where as SN 35.23 is the Buddha's debunking or redefining of 'The All' for Buddhist purposes.
It is important to know that certain pre-Buddhist Brahmanistic terms, such as 'The All' and 'nama-rupa' can have dual & different meanings in the suttas, namely, the original Brahmanistic meaning & the revised Buddhist meaning. For example, the Brahmanistic meaning of nama-rupa is 'name-form' where as the Buddhist meaning of 'nama-rupa' is 'mentality-materiality'. Thus in suttas directed to Brahmnins (example SN 7.6; DN 11; MN 49 and DN 15), nama-rupa retains its Brahmanistic meaning. Similarly, in MN 49, the term 'The All' retains its Brahmanistic meaning (rather than is the Buddhist meaning found in SN 35.23).
That the famous Western scholars such as Thanissaro, Bodhi, Sujato, etc, do not distinguish two meanings of nama-rupa and cling to the literal Brahmanistic meaning of 'name-form'.
This said, the monk Sujato provides his opinion at: 'Nibbana is not viññāṇa. Really, it just isn’t.', which is contrary to Thanissaro's ideas. In short, Sujato's view appears to be viññanam anidassanam is an immaterial jhana (although I personally may not agree).
While I have not examined the matter in depth (given it is an unimportant teaching), my initial impression is viññanam anidassanam is merely a teaching to Brahmins challenging them to abandon their existing ideas & doctrines. In short, it is later-day Buddhist propaganda typical of the dodgy suttas found in the Digha Nikaya. Most scholars accept the Digha Nikaya was compiled for the purpose of converting Brahmans to Buddhism.