x11-libs/openmotif:2.2 now contains a backwards-compatibility library which only installs shared libraries (but no header files). gvim should therefore depend on openmotif SLOT 0: >=x11-libs/openmotif-2.3:0 Problem is that this requires at least EAPI 1. However, the dependency is handled via vim.eclass which also supports EAPI 0.
Good news -> I was recently able to clean out a bunch of ancient vim ebuilds, so all the ebuilds that now use vim.eclass are EAPI=3 Adjusted vim.eclass to only allow EAPIs with slot deps, and also adjusted the openmotif dependency.