> there are open legal questions about whether the GPL and its variants are enforceable.
At this point in history, there are multiple legal cases where GPL violators were taken to court and lost or settled. See: BusyBox and Linksys/OpenWrt.
GPL v3 also has a nice clause that allows companies to "repair/cure" their non-compliance.
> Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
GPL v3 also has a nice clause that allows companies to "repair/cure" their non-compliance.
Red Hat also has a good blog post about their view of using the legal system to enforce compliance: https://www.redhat.com/ja/about/gplv3-enforcement-statement