Something just occurred to me. Perhaps it would be most flexible to allow guilds to buy permission to include members of particular civs? That way neutral-only guilds could stay neutral-only, Kara guilds could choose to accept Matis and Tryker, and indifferent guilds could choose to accept all civs. I'm not actually clear on what other benefits civ allegiance has for guilds, though, so I don't know whether this should be made more or less difficult than simple allegiance.
