As somebody said, if a old and renowned scientist says something is possible, he's most likely right; if he says something is impossible, he has a very serious chance of being wrong.
Gotta keep in mind that there are already several extant well-funded and highly motivated organizations devoted to studying the brain... and they're not doing whole-brain ephys.. they're doing advanced fluorescent microscopy
What I'm saying is that you can ignore and disparage the experts all you like and sometimes get away with it. But then sometimes reality sets in.
[0] https://www.statnews.com/2020/02/25/cdc-expects-community-sp...
[1] https://www.whitehouse.gov/briefings-statements/remarks-pres...
and when an md/phd says something is "impossible today" and a salesman who thinks biology is a "software problem" says it's possible for the right price, I know who I'll bet on