I believe the legal counter to this which is slowly starting to emerge is 'We're not ordering you to divulge your password. We're ordering you to decrypt the drive. We quite specifically don't want, or need, your password, nor do we care if the drive is encrypted with a passphrase, biometrics, physical token, whatever. We're just ordering you to decrypt it.'
Much like your 'papers' are immune to unreasonable search and seizure, but are subject to reasonable search and seizure, i.e. with a duly sworn out warrant and all that, so are your digital papers. I think this is the correct result.
I believe that, if the cops find a file in a locked file cabinet, said file being labelled 'Plans to murder my wife' and full of, well, plans to murder your wife, you don't get to have them declared inadmissible under the fifth; you get to refuse to answer questions like 'did you create these plans' and 'did you carry out these plans.' Seems to me that a directory full of documents, said directory being labelled 'plans to kill my wife' would be treated the same.