The linked W3C mailing list[1] provides some interesting discussion, as well as a blog post from Jan outlining this attack[2].
The conclusion: security benefits of CSP outweigh cons.
[1] http://lists.w3.org/Archives/Public/public-webappsec/2014Feb...
[2] http://homakov.blogspot.de/2014/01/using-content-security-po...