1. Does an AI "reading" source code that has been otherwise lawfully obtained infringe copyright? Is this even enforceable?
2. Why write a new license rather than just adding a rider to the AGPL? This is missing language the AGPL uses to cover usage (rather than just copying) of software.
To the extent that this has been decided under US law, no. AI training on legally acquired material has been deemed fair use.
The operative words are the last four there. GPL, and all other software licenses (copyleft or not), can only bind you as strongly as the underlying copyright law. They are providing a copyright license that grants the licensee favorable terms, but it's still fundamentally the same framework. Anything which is fair use under copyright is also going to be fair use under the GPL (and LLMs are probably transformative enough to be fair use, though that remains to be seen.)
Arguably, at least in the US, it has been seen. Unless someone comes up with a novel argument not already advanced in the Anthropic case about why training an AI on otherwise legally acquired material is not transformative enough to be fair use, I don't see how you could read the ruling any other way.
Honestly with how much focus there tends to be on *GPL in these discussions, I get the feeling that MIT style licenses tend to be the most frequently violated, because people treat it as public domain.