It should be >=app-text/poppler-0.12.3-r3[cairo] since the virtual(s) are going away. The problem here is that I have no clue about ruby's eclasses, and their status of EAPI="2" support for USE deps. Please fix. Thanks.
Fixed. The old ruby eclasses (used in 0.19.1) are unaware of EAPI versions. The new ruby-ng eclasses (used in 0.19.3) are EAPI="2".