I think you may be overestimating the usefulness of a third-party beneficiary approach. There are two issues with it: (1) Isn't SFC vs the only case where how

I think you may be overestimating the usefulness of a third-party beneficiary approach. There are two issues with it: (1) Isn't SFC vs the only case where how third-party beneficiary law applies to GPL enforcement has come up? That case has not yet gone to trial. The third-party beneficiaries have only been considered in the context of motions of summary judgement. The court ruled that this will have to be determined at trial. (2) You can only have a third-party beneficiary to a contract when there is a contract. The defendant should be able to defeat a third-party beneficiary claim by saying that they did not agree to the license. They saw code they wanted to use and thought it was public domain or thought their use would be covered by fair use or decided that they would go ahead and infringe its copyright because they thought the risk of the copyright owners suing was negligible. That approach would have some risks if the copyright owners later do sue, because it would be tantamount to admitting their infringement was willful which can greatly increase statutory damages.