I agree, I don't doubt that Shiver was around. If some of the stuff that is discussed over at the Wolf Age forum is true, she may have been on the side of light, a friend/lover of Damas. Too many theories for me to understand though. :). New Fallen Lords would be good, they were (for me) the best part of Myth even though you didn't see much of them (only Soulblighter). Of course, we did get to see the Watcher's inanimate ass.
I agree about the Smiths, I mean, what the hell could you do with them in gameplay? Hearing about the Tain etc. would be cool though. The Spider Cult on the other hand could open some cool unit possibilities, depending on their relationship with actual arachnids. Can you imagine Spider Cavalry?
Myth:TFL left Myth II for dead in story quality and suspense, but strangely I've always preferred playing MII despite having played Myth first. Weird how it turns out.