xemacs can use lesstif instead of motif. I'll apply a patch to enable lesstif support over motif with lesstif use flag.
Created attachment 42006 [details, diff] xemacs-21.4.15-r2.ebuild-lesstif.diff Note that lesstif is not keyworded alpha (it is keyworded ~alpha), so you need to stablise it before commiting the patch.
this is obsolte, you can now use motif-config (currently ~arch) to switch your motif version