There is nothing logically wrong with an experiment like that. But there is no economic / political path where this happens. Even, say, there were a massive political turnaround in the next election cycle that could push something like that, just the international treaties would make this difficult enough.
I thought about this more, and I noticed something else wrong with that version of the experiment. The compromise has to be at the other end of copyright term. It's crazy to remove all authorial rights from anyone actively working today.
Something more like: For the next 5 years, all copyrights before 1970 become subject to the "author's lifetime" standard, and nothing else changes. If the experiment fails, then those rights are automatically restored to any corporations/estates that owned them. (With some mechanism to shield copies made in that interim from future litigation.)
That sounds like a more balanced version of the experiment, and I still think it has very little chance of coming to pass. I'm not good with Bayesian formalism, but my priors are something like: status quo most likely, permanent (but small) concessions to get a little bit more old stuff into the public domain next most likely, all other options highly improbable.
Finally: maybe it's sensible to try to shift the Overton window by calling for the abolition of copyright. But I don't know how one does that kind of thing ethically if you don't really want to go that extreme.
