Yeah, it's a heck of a lot of work. First, you have to change the creature type itself from devil to demon. You need to know all the traits of both creature types so it matches up. If the succubi has traits associated with the Hells, such as "hellfire touch" or somesuch, that will need to be removed. If fiends can still summon other fiends in 4e, obviously that would need to be changed. Now I'm real comfortable with monster design, so I'm sure I could pull that off, but since the new version is being geared towards folks who don't want to devote that amount of prep time, this is a real blow to them.