The name of this ebuild is missleading, because this package is far from being just an engine. It also holds some gtk themes and metacity themes (which is fine, most gtk-engines-* do this as well), but -more notably- it also holds an icon theme. I suggest renaming the ebuild to just "nimbus". And changing a bit the description of the package. Reproducible: Always Steps to Reproduce: I'll submit a patch soon.
Created attachment 264365 [details, diff] Patch to convert gtk-engines-nimbus-0.1.4.ebuild into nimbus-0.1.4.ebuild
Comment on attachment 264365 [details, diff] Patch to convert gtk-engines-nimbus-0.1.4.ebuild into nimbus-0.1.4.ebuild Different patch was committed to tree.
x11-themes/nimbus-0.1.7-r1 in Portage, and moved over