net-libs/libsoup-gnome-2.48.0::gnome lacks multilib support which is required by, for example, net-libs/rest::gentoo. (As a side note it looks like net-libs/libsoup is listed twice in dependencies of net-libs/libsoup-gnome)
Sorry - it looks like net-libs/libsoup has multilib - only net-libs/libsoup-gnome misses it.
This was fixed a while ago.