But from a higher-level thinking point of view, neither of the requirements you mention mean a stub is necessary. I know this is a little nitpicky, but e need to step back from things like this to realize that the entire premise of a stub is only required because of previous decisions in the system.
The only things the user actually needs is (1) a way to find a seat, and (2) a way to verify their identity to agents. The stub happened to satisfy those requirements, but they could easily be solved in different ways (like Southwest has done).
That's the biggest problem with this entire article, it's only thinking about the last step of design decisions, so it's not going to come up with very innovative results.
There's too much money to be made in selling premium seating. Which Southwest also does, in case you're unaware.
Plus, with assigned seating it is possible to run simulations which will give more efficient boarding sequences.
On the identity side you already have to travel with identification and that can be used a lot of the time. Things can get complicated (eg being rebooked by another airline), lots of queues, many flights leaving at similar times where the stubs are helpful because people can be helped and processed a lot quicker. The stub is something that can be consistent between passengers whereas passports, drivers licenses and other forms of identification are all over the place.
I've only had them scan the boarding pass and give the whole thing back to me in its entirety.