Hi Digger, I quite agree -- that consciousness usually changes when dying (especially when actively dying), that those with dementia can go into a variation of this state long before dying, AND definitely that most people are not comfortable being around this state. Most people -- as trained by our culture -- feel uncomfortable if they are not 'doing' something (engaging in an activity or conversation); and stop visiting when they can no longer 'do' something with the Death Journeyer -- especially if the dying process is elongated (as it is with dementia).
As a Quaker, I am lucky to have weekly experience with connecting into the quality of silence in our Meeting for Worship -- which is definitely a form of 'holding space', as well as 'being present' and 'listening within'. Although most Quakers would not define that as 'listening to the within of another person', I believe that that is also quite possible. When a variation of that happens, we call it a 'gathered Meeting for Worship' -- where we have gently and quietly achieved 'holding space' for all of us gathered. Again, you are quite right -- even though Quakers attempt to do it on a weekly basis, and have developed some very generalized language for it, it would still be very difficult for any of us to then define exactly what we are talking about (i.e. details, specifics, etc., or how we KNOW that the Meeting is gathered).
I am also Wiccan -- and we also have some general language for a similar state of connectedness, and equal difficulty defining it (outside of symbology that would not necessarily be useful to others): I suspect that most religions do -- especially the more mystical variations of, or practices within, them. But then, this makes it more difficult for people of different religions, or those who don't allign with any religion, to share a language with which to talk about this 'difficult to describe' state.
In my own experience, gentle chant-singing is a more active/doing way to make this connection (and something that family members often do just spontaneously) -- a more overt way of not only 'holding space', but 'listening to the within of another'; and even reading out loud can make this connection. That may seem strange because of both of these have the appearance of 'sound covering silence'.
There certainly is lots of anacdotal evidence that the Death Journeyer (even if asleep or in a coma) is aware of this kind of 'presence' and hears what is offered -- although they are not processing it in the same way that they would if they were in awake/alert consciousness. I suspect that the Death Journeyer is mostly picking up the overall 'sense'/quality of what is sung/read; and therefore, the most important element of this more overt kind of 'holding space' is the companions' intention.
If focused properly, the singing/reading can project, and connect in, an intention of truly and deeply 'being with' the Death Journeyer. And while my experience leads me to believe that what is sung/read is important as well (that the DJ connects to the quality/intent of the music/rhythm/words of either), it is foremost the intention of 'being present' and 'holding space' that the DJ connects with, AND supports whatever inner 'work' (again, lack of language here) they are doing as their body and psyche prepares for death.
Again, in my experience, the 'thread' or 'cradle' of connection achieved can give the companion some sense of what the DJ is experiencing, and be able to respond to it ('sharing' being a 'two-way street') -- but again, as you say, we really don't have any language for the process of connecting itself (whether through the medium of singing/reading, or being silently present) or what the DJ or the companion gains from it.