You asked for thoughts, here you go! This isn’t an attempt to answer the OP, it’s just me jotting down thoughts, trying to put it together in my mind.
When I consider DO, I see it kind of as a mechanism, a system of processes in place which activate in a chain. When ignorance is present, the systems that are in place act as a domino effect, a chain reaction.
Since you need both a physical brain and functions of a mind to process the raw data captured by a sense organ, you can’t continue the chain of DO without namarupa and viññanā. Namarupa includes phassa but does not include consciousness.
Analayo explains name-and-form thus:
“Form” represents the material side of experience.
“Name” stands for the functions of the mind apart from viññanā . In SN 12.2 the mechanism of “name” stands for the following mental factors:
“Phassa” ensures the conjunction of the other factors in experience, their coming together in a particular time-and-space-instant with the material dimension of contact taking the form of experience of resistance (patigha) and the nominal dimension of contact taking the form of designation (adhivacana).
“Viññanā” is the mind’s ability to be conscious of something.
(end of quoting Analayo)
In MN 148 the Buddha says “And what is consciousness? There are these six classes of consciousness. Eye, ear, nose, tongue, body, and mind consciousness. This is called consciousness.”
It could be that viññanā are simply the regions of the brain which are stimulated by by data sent by sense organs. These are the primary sensory areas which are the primary cortical regions of the sensory systems in the brain, the regions that light up in an fMRI when stimuli arise.
The classes of consciousness that the Buddha described rely on namarupa to do something with that data, thus the mutually reciprocal relationship between namarupa and viññanā.
In this case I’m finding it helpful to work backwards through DO.
You can’t have old age, sickness and death without rebirth.You can’t have rebirth without the process of kammabhava.
You can’t have kammabhava without clinging.
You can’t have clinging without craving.
You can’t have craving if vedanā has not arisen.
You can’t have arisen vedanā if there has not been phassa.
You can’t have phassa if there are no bodily sense organs to capture data.
Since you need both a physical brain and functions of a mind to process the raw data captured by a sense organ, you can’t continue the chain of DO without namarupa and viññanā.
Note: I think it’s interesting that phassa (and vedana) are each in DO twice.
Each as a link and both in nama within namarupa.
I wish I were better able to express my thoughts.