Is that a paper from 2005 about a system designed in 1997? History is excellent for research but in the decades since, many things have changed.

Some of those downsides are positives (immutable, easily copied) others aren’t accurate, for example here’s the Mumbai metro in 2023 with qr entry gates https://youtube.com/shorts/TxbEgEzY9J8?si=s3gE-7_xbCbDoQ1d

Or that a 100% available central ledger is needed (it’s not).

That Qr code systems are in use today in some of the busiest locations would probably be the most succinct counterpoint though.