However, it's not actually the laundering angle I am concerned with here entirely, it's whether we're turning FOSS codebases into potential legal toxic waste dumps that we will have a hell of a time cleaning up later.
The previous Conservancy post, which @bkuhn linked upthread, indicates that Conservancy does indeed consider the matter unsettled.
Current LLMs wouldn't "default to copyleft", since they also include all-rights-reserved mixed in there. If the result of output of these systems is a slurry of inputs which carry their licensing somehow, their default licensing output situation is one of a hazard.
I note that @bkuhn and @ossguy seem to be hinting at hoping a "copyleft based LLM" with all-copyleft output it a winning scenario. I'm going to state plainly: I believe that's an impossible outcome.