More fun with Title 17 USC
''joint work'' is a work prepared by two or more authors
with the intention that their contributions be merged
into inseparable or interdependent parts of a unitary whole.
Copyright in a work protected under this title vests initially
in the author or authors of the work. The authors of a joint
work are coowners of copyright in the work.
So, I wonder, how many open-source works qualify as joint works? There
would certainly be some benefits (e.g., making clear who can sue for
copyright infringement --- any of the authors) but some serious
downsides too (like any of the authors being able to grant
non-exclusive licenses, without the other authors' consent).