First and foremost, thanks for presenting this topic, providing a link and, more broadly, starting a discussion.

While I only have limited knowledge of TNGS to write a proper reply, there is one aspect of what you wrote that I deeply disagree with (although it probably means very little to the validity or not of TNGS): the concept of a primary versus higher order consciousness.

In short, I believe there is only a primary consciousness and, believing we humans share a deeper level of consciousness than other animals (for whatever reason) is just we being egocentric.

In more detail, I took sign language classes back in school, and part of the curriculum was deaf culture. I got to say it was quite the experience. We, hearing individuals, have a tendency to assume everyone thinks like us, so we also tend to overestimate some human traits, such as language and our internal monologue, that we can't readily verify on other beings (e.g., do dogs have a language?).

Now, think about it, does a born-deaf person has an internal monologue?

What do you believe goes on their head while they think?

Repeat this little thought experiment by picturing a born-blind person. What do you think changes compared to yourself or the born-deaf individual?

How can we ever know what goes on someone else's mind?

Think about it.

Then, consider a barking dog, a playful set of dolphins, and an octupus. How can you be so sure they lack a language (even rudimentary) to assume they lack a higher-order consciousness that we humans acquire because we have the gift of language?

That's why I believe there is just a consciousness, not a two-tiered structure that only us humans happen to have attained the second tier. We probably just happen to have a better brain-to-body-size ratio to be smarter than most.

About "the attitude seems to be that we still know next to nothing about how the brain and consciousness work." You are probably right about this, despite how little concensus there is on these topics. What I find funny is how the media portrays much of AI advancements of late as "we are nearing the doom of civilization" while we most certainly are much closer to nuking ourselves up than having some AI take over the world.