Duane has had an answer from the RSC's press office regarding the whole Cardenio announcement. I'll let you visit Shakespeare Geek for the full clarification but it isn't a new find or authentication of an old text but a production based on that later translation called Double Falsehood. It all seems to be a bit of a misunderstanding.
In other news though, according to someone commenting on the blog, Arden are currently preparing an edition of that play for publication, edited by Professor Brean Hammond, Head of School of English, University of Nottingham. There's a transcript of a television interview with him here which seems to suggest it will be published under their Shakespeare banner and that they are making a case for it having a certain canonicity.
It's not listed in their catalogue yet though. Interestingly, Arden are beginning a new series in 2009 of drama from the same period in their distinctive style, so perhaps if they can't authenticate Double Falsehood they'll put it there instead.
Frankly, this is all getting far too confusing. I think I'll stick to Hamlet. So about the placement of 'To Be Or Not To Be' ...