Would be a treat if there were bonuses to be had from the other planes. Such as getting kings under the mountain by recruiting from Pedoseion' citidel in Agartha. Or knick the dwarves of the four corners from dominions and make them available from the elemental planes. Setting up a dwarf hold in Kokytos was a hoot but there really wasn't that much to gain from it for the effort, you can't even upgrade your freespawn workers down there.

There's only so much that can be done with CoE modding.