I suspect it would take a long while for an open source project to run into this limitation, especially if the tabs were distributed soulseek-style.
Has anyone attempted to make a fair use for education argument about this? Tabs aren't so much an actual creative work as instructions for how best to play a work. Because there's no timing information it's often impossible to reconstruct the actual music just from them.
Chords have even less information, a guitar chord transcription may have no resemblance to the notes actually played in a recording.
The transcriptions (created by people) are always going to be seen as derivative works, unfortunately. It doesn't matter how closely it matches the recorded performance. But the fact that text-based tabs remained online (at least more so than transcriptions, powertabs, etc.) is likely because of the lower fidelity.
It's not just that the transcription is a (transformed) reproduction of the original piece. The record companies have the (exclusive) right to (sell) the transcriptions, sheet music, etc. of music they hold the rights to. They have that right, regardless of if they are actively or ever going to actually publish any.
I would guess a fair use defence would be feasible in the right case, but I'm not sure if that was ever tested in court. Most of the operators of tab websites were just people, they didn't stand a chance. If I remember correctly, Ultimate Guitar was/is one of the few sites that was big enough to negotiate with the MPA.
Has anyone attempted to make a fair use for education argument about this? Tabs aren't so much an actual creative work as instructions for how best to play a work. Because there's no timing information it's often impossible to reconstruct the actual music just from them.
Chords have even less information, a guitar chord transcription may have no resemblance to the notes actually played in a recording.