The "katepart" component which rkward uses for its IDE was split out into a separate Gentoo package with KDE 4.7.0. So if any version of rkward is being built against KDE>=4.7.0, kde-base/katepart must be pulled in as a runtime dependency. rkward will, oddly enough, compile without katepart being installed, but it will segfault as soon as the application is started. Reproducible: Always
Fixed, thanks!