By adding KEYWORDS="~amd64 ~x86" to all of the enlightenment 17 packages: embryo, eet, edb, evas, ecore, edje, e, exml, epeg, epsilon, esmart, e_modules, ewl, engrave and e_utils I was able to get it running, and quite stable on an amd64 system.
All the e17 live cvs ebuilds are -*; if you want to use them, put cat/pkg -* into package.keywords.