Is it obvious? Waymo has hundreds of driverless taxis in SF where you literally cannot sit in the driver's seat. Stuff that consumers can currently get their hands on isn't really driverless but the tech exists now.
For cars like Waymo/Cruise/etc, those are Level 5 to my knowledge (with restrictions for location, I guess). You can't sit in the drivers seat, so how can the passengers possibly pay attention or do anything? This study is talking about drivers (in the drivers seat) and Level 3/4 technology. So, what Mercedes is advertising and other car manufacturers are aiming for in the future.
Level 5 is essentially defined as L4 with an "unlimited" ODD, not a meaningful level on its own. Waymo and Cruise are L4 systems, but you could build an L4 system where people were able to drive if you wished.
I get that it's defined that way, but it's not, practically speaking, the same. The article is about a driver having L3/L4 tech. Waymo/Cruise are not allowing that. So you truly can relax/nap/do work email... because what else would you do?
Yes, and the article quotes people that are really only talking about L3, even though they use the word "L4".
One of the defining features of L4 as everyone else uses that term is that you are not required to take over, even in emergencies. L4 capabilities don't prevent you from voluntarily taking over, it's simply not required that you be able to in order to operate the ODD. Both Cruise and Waymo operate test fleets with drivers who can take over, incidentally.