[oscillatingfans]

A system cannot switch the service type to "prevent DDoS from spoofed IP packets" though.

The authors are not arguing against packet switching; they're questioning whether point-to-point still applies when a majority of the Internet is used for accessing content. CDNs aren't cheap, a content-centric network (e.g., https://en.wikipedia.org/wiki/Named_data_networking) could substantially increase efficiency.

[contingencies]

There are many effective DDoS resistance strategies. However, if you had to build those costs in to the core of the internet, then there is a fair argument that it may never have taken off as overheads would have been too high.

For the NDN concept, again the whole point of IP is that you can implement it on the same base: Upgrade cost of network complexity: The Internet has smart edges ... and a simple core. Adding an new Internet service is just a matter of distributing an application ... Compare this to voice, where one has to upgrade the entire core. - RFC3439 (2002)