As far I cannot build epiphany in Gentoo with webkit backend. Adding webkit use flag would be a nice idea. PS. Possibly it should be implemented first in gnome overlay.
Patches are more than welcome :)
Created attachment 156821 [details, diff] 0001-Added-a-copy-of-www-client-epiphany-2.22.2-from-port.patch Something like that?
Created attachment 156823 [details, diff] 0002-Added-webkit-support.patch Those are git patches...
I'm afraid that they are not tested yet however...
*** This bug has been marked as a duplicate of bug 220084 ***