The ability to terminate transfers and licenses is covered by 17 USC 203 (plus some other sections with different timetables and rules for transfers/licenses th

The ability to terminate transfers and licenses is covered by 17 USC 203 (plus some other sections with different timetables and rules for transfers/licenses that occurred before 1978). There's an interesting and formally unresolved (because the applicable window for the earliest "copyleft" works hasn't yet arrived, for one thing) question about how this interacts with things like CC0, GPL, and more informal licenses to the public at large. The law requires the termination to fall into a specific 5-year window, with advance notice in writing (and it must be multiple years in advance), served specifically to the person whose rights are being terminated. The sheer logistics of trying to terminate a license granted to the world are therefore pretty difficult, but you could imagine termination targeting just a handful of lucrative targets. (Even then, when does a generally-available license "start"? When it's first offered? When the specific user first accesses the work? Is the timeframe "refreshed" every day the license is still on offer? This provision really wasn't written with these kinds of licenses in mind.)