app-editors/jove-4.16.0.70.3 with USE=-X installs and works on amd64. However, with USE=X the optional "xjove" binary cannot be installed. It requires x11-libs/xview, which is unlikely to be available for 64bit architectures anytime soon. See <http://physionet.caregroup.harvard.edu/physiotools/xview/>. Therefore, in addition to the keyword, we would also need an entry for "app-editors/jove X" in amd64/package.use.mask.
Thanks welpie