Niva Elkin-Koren has published "Can Formalities Save the Public Domain? Reconsidering Formalities for the 2010s" in The Berkeley Technology Law Journal.
Here's an excerpt:
In essence, formalities advocates argue that current copyright law protects too many works, and shifting back to an opt-in regime would help restore the balance in copyright law between incentives and access. Restoring formalities would arguably expand the public domain by increasing the number of works in which copyright is not affirmatively claimed. It has been further suggested that works of unknown authorship are underused. 8 This is due to uncertainty about whether they are protected by copyright or not, which creates a chilling effect. A notice requirement would signal to potential users which works are protected by copyright. A notice would also generate the information necessary for licensing, thereby facilitating the clearance of rights and reducing the problem of orphan works.