(Personal communication from Christopher Shaw PhD, with his permission.)
I think we need to start posing thought experiments in the absence of actual data.
To begin, I've spent a lot of time in the army, so my thinking often goes into the army mode of asking the "so what" questions.
Such as: according the the study by Bahl, at least in mice, the mRNA construct in some form gets into the brain. So what? Does it get into any neurons, or glia, or both, or not? If not, fine. If it is found in any neural cells and in what amount and where, so what? Does it make spike protein? So what? How do microglia respond to this? Do the proteins stay in the cell or wander around? If the proteins stay in the neural cells, are they degraded or do they have the capacity to form beta sheets?
All speculation. Maybe none of this will happen, which would be good. What, however, if it does? So what? Will some of those who have the mRNA in their brains have neural consequences? How long will these take to emerge, if at all? What happens if you give the mRNA vaccine to 3/4ths of Americans (and Canadians), and something later happens? At present, we can't do anything useful for AD or ALS patients, somewhat better for PD. So what happens to the medical system if the numbers of age-dependent neurological diseases increase? Dennis Glanzman, former head of the Broad Institute gave a very sobering talk about 10 years ago at SfN in which he stated that the current pace of AD alone had the potential to break the system.
So lots of so what questions that need some basic studies to answer.